Hey Dean, I really appreciate the question –– it’s actually a really loaded question. It’s one of those questions you can talk about for hours and still not be done discussing it. In fact, all the epistles are basically about answering this question in some way.

I’m assuming that when you ask, ‘what attributes and outward actions suggest a true Christian?’, you are not excluding the belief in necessary doctrines like the existence of God, the Trinity, God’s goodness, et cetera, since those beliefs are clearly necessary to be a true Christian (especially given the fact that true belief demands corresponding behaviour). Instead, you are simply asking: Even though people may claim these beliefs as their own, how can we discern the sincerity of their claims based on their character, emphases or patterns of behaviour? That, my friend, is a good question!

The Lens of Christian Life

It’s important not to be presumptuous or judgmental, here, considering grace and mercy triumph over judgment and God is the final judge of all (James 2:13). It’s also important not to expect the answer to this question to be like an on-and-off switch or checklist of dos and don’ts. I say this because there are things Christians ought not to do (Galatians 5:19-21), and we are called to be obedient (1 John 5:2-3), and because of that dynamic we may have categories of godly and ungodly behaviour that might force us to lump a true Christian over here and a false Christians over there. This tension will always be with us until Christ returns. But it is not our earthly mission to separate the sheep from the goat, or the wheat from the weeds, that right is reserved for God (Matthew 25:31-33; 13:24-30). In other words, we cannot condemn (Jude 1:9). So, we have no ultimate authority in this regard. That said, we do possess the Holy Spirit, which helps us identify and assess whether someone is on the right path or not. On that, our perspective of the path is vitally important.

The Christian life is about growth in Christ, and growth in Christ begins with faith, repentance, and forgiveness. When we imagine a tree, we typically don’t picture a seedling. So, then, should we call a seedling a false tree? Well, no. It’s just not mature yet. This is how the apostles approach the congregation, also. Those of weaker faith are like infants who need “spiritual milk”. Consider Peter’s words carefully, “So put away all malice and all deceit and hypocrisy and envy and all slander. Like newborn infants, long for the pure spiritual milk, that by it you may grow up into salvation—if indeed you have tasted that the Lord is good.” (1 Peter 2:1-3) Consider Paul, “But I, brothers, could not address you as spiritual people, but as people of the flesh, as infants in Christ. I fed you with milk, not solid food, for you were not ready for it. And even now you are not yet ready, for you are still of the flesh. For while there is jealousy and strife among you, are you not of the flesh and behaving only in a human way?” (1 Corinthians 3:1-3) Notice that Paul still calls them “brothers” in Christ despite their infancy in the Spirit, moral failings, and fleshly conduct. He does not distinguish true from false Christians based on their outward actions alone, even though many are clearly straying. He knows repentance is still on the table and faith can grow slowly, that we each have a “proportion to our faith” (Romans 12:6). Our mission, then, is to grow and be mature in the faith (Hebrews 6:1-3).

In another way, should we say that a seed is a tree? Also, no. The tree is hidden inside the shell and hasn’t broken through the husk; it hasn’t started to grow yet. If the seed sown in a person’s heart is the word of God, and this seed is what grows into a seedling (infancy), it will take some time for that seed to grow. It will take time to see the fruits of God’s work come through a person. For when the seed does start to grow, we don’t know if the seed is growing until it has broken through the soil, until we can see outward action. Yet, the attributes of Christ are patiently growing under the surface. One of those attributes is repentance: the root of the Christian life. From repentance springs forgiveness. Therefore, we, too, must be patient and gracious and merciful in our discernment when attempting to identify true Christians. There are seeds, as small as mustard seeds, there are seedlings, there are saplings, and there are oaks–––fully grown in the faith. Some trees grow slower and others faster.

Now the parable is this: The seed is the word of God. The ones along the path are those who have heard; then the devil comes and takes away the word from their hearts, so that they may not believe and be saved. And the ones on the rock are those who, when they hear the word, receive it with joy. But these have no root; they believe for a while, and in time of testing fall away. And as for what fell among the thorns, they are those who hear, but as they go on their way they are choked by the cares and riches and pleasures of life, and their fruit does not mature. As for that in the good soil, they are those who, hearing the word, hold it fast in an honest and good heart, and bear fruit with patience…. He indeed bears fruit and yields, in one case a hundredfold, in another sixty, and in another thirty (Luke 8:11-15; Matthew 18:23)

Visibility of Spiritual Growth

With that groundwork laid, I can address your question more directly: What does spiritual growth look like? What should we expect to see? As you ask, what are the attributes and outward actions of a true Christian?

In Galatians 5, Paul contrasts works of the flesh against the fruits of the Spirit, which is a list of godly character traits. It is not an exhaustive list but is nevertheless essential:

But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, self-control; against such things there is no law. And those who belong to Christ Jesus have crucified the flesh with its passions and desires. (Galatians 5:22-24)

As I said before, the possession of these traits/attributes must be understood as one who is growing in Christ, as a seedling maturing into an oak and bearing fruit. In Colossians 3:12-17, Paul expands this understanding of what good Christian character ought to possess: compassionate hearts, humility, meekness, wisdom, a forgiving and thankful heart. And elsewhere: perseverance, discipline, judiciousness (sense of justice), endurance, obedience, contrition, loyalty, humbleness, respectfulness/reverence, hopefulness, all amidst persecution (cf. Romans 5:3-5). Not every Christian will possess all these attributes at once, and some will bear more fruit in one area than another. Some will be richly saturated with all of these, others only a little. Therefore, failing to fully possess or express these traits or to do them well does not disqualify you as a Christian. The grace of the gospel cannot be undermined by our own moral tolerance, partiality, or inadvertent presumptuousness (to think we know better). I think it wise to always air on the side of grace. And the apostles seem to do the same. C.S. Lewis was right when he said, “When a man who accepts the Christian doctrine lives unworthily of it, it is much clearer to say he is a bad Christian than to say he is not a Christian”. Therefore, a person who professes Jesus Christ as Lord and saviour and seems to be on a path of living like Christ is considered Christian, a brother or sister in Christ. I see no harm in taking them at their word. We include them as part of the Christian community, even if they have deep faults or sin. God is the ultimate judge of our eternal lives, a territory we ought not broach.

For that reason, we have to observe and discern a person’s trajectory of character, not just individual instances where they flounder or do well. Who better to do this then God? Who better to grow our discernment than God?

For though by this time you ought to be teachers, you need someone to teach you again the basic principles of the oracles of God. You need milk, not solid food, for everyone who lives on milk is unskilled in the word of righteousness, since he is a child. But solid food is for the mature, for those who have their powers of discernment trained by constant practice to distinguish good from evil.

Therefore let us leave the elementary doctrine of Christ and go on to maturity, not laying again a foundation of repentance from dead works and of faith toward God, and of instruction about washings, the laying on of hands, the resurrection of the dead, and eternal judgment. And this we will do if God permits. (Hebrews 5:11-14; 6:1-3)

Maturity in the Spirit grows discernment, which helps us understand a Christian’s trajectory of character–––the path the leads to eternal life or the path that leads to death. The Spirit helps us discern those who love God from those who kinda-sorta do or simply don’t (but, perhaps, say they do). It discerns the living and growing from the static and dead. A maturing Christian, then, is also a true Christian, they are not quickly overtaken or succumb to a life of sin. They have roots, so to speak, deeply ingrained roots that only grow deeper in relationship. What, then, grows maturity in the faith?

The Substance of Growth

If Christ desires us to mature from spiritual milk to solid food, what can be more solid than the very foundational attribute the Christian life rests upon? Paul boils down the greatest attribute of our Christian life to love, he even puts it above faith (1 Corinthians 13:13); John says Christians must love one another to be Christian since God is love and God’s love is perfected in us through our love for one another (1 John 4:19-21); Christ also says that the world will know Christians by their love (John 13:35); Christ says you cannot have eternal life unless you love God and neighbour (Mark 12:29-31; Luke 10:25-27); Christ came and died and rose again because he loves us (John 3:16). So, what is love?

Love is patient and kind; love does not envy or boast; it is not arrogant or rude. It does not insist on its own way; it is not irritable or resentful; it does not [count or] rejoice at wrongdoing, but rejoices with the truth. Love bears all things, believes all things, hopes all things, endures all things. Love never ends. (1 Corinthians 13:4-8)

This is, perhaps, the most famous description of love. Love is so grounding that it not only affects our whole being but everyone around us. It unifies the essence of who we are with others. It is the basis of our relationship with God and our relationship with believers. The love that comes from God saturates and intensifies and brightens all those fruits of the Spirit mentioned above, it is a self-sacrificial love that, as Aquinas puts it, “wills the good of the other” at the expense of one’s life, while they are still sinners (Romans 5:8). It is what it means to live like Christ. Church history from the apostles to their disciples bears witness to countless conversion stories of love–––missions to the Vikings of Scandinavia, Hurons of Canada, tribes of South Africa, et cetera. Missionaries travelled to pagan nations and were brutally persecuted, tortured, and killed for the gospel. They sacrificed their life to show other’s Christ’s love through them and pagans saw God’s love through their works and came to Christ because of it. Even though these nations were very spiritually dark, they could still see God’s love through them. They received the seed. Our call is to manifest and express that self-sacrificial agape love in our lives–––that is the mark of a true Christian. It is that mark which we can look upon and say, with all assurance, is the mark of a saint.

Final Remarks

That said, we are not all missionaries. We are not living in persecution. On that, Paul does advise: “Examine yourselves, to see whether you are in the faith. Test yourselves. Or do you not realize this about yourselves, that Jesus Christ is in you?—unless indeed you fail to meet the test!” (2 Corinthians 13:5) It is vitally important we self-reflect on what Paul is asking, here. It can really help us better understand and discern our own spiritual direction as well as others, so that we are not self-deceived: Do you have a personal relationship with God? Are you consistently persevering in the Spirit in prayer and supplication? (Ephesians 6:17-18) Is our faith in Christ getting stronger? What lifestyle were you living and where are you now? Are you living for God’s house or your own house? Does everything you own belong to God? Do you love fellow believers and your neighbour as yourself, or do you just tolerate them? (1 John 4:19-21) Do you pray for those who hurt you, for their own good, full well knowing that they are spiritually sick? Is Church on Sundays or is it every moment? Are you struggling or battling with sin or just letting it slide? Do we help the sick and needy, orphans and widows? Is humility necessary or just important? How’s your prayer life–––could it be more active? Do you love God with all that you are, all that you have, all that you can, and all that you could? Now there’s way more we could ask, but I hope this gives you an idea. There is no universal rubric for discerning character, it is completely contextual and relational. A true Christian will not only desire to maximize the goodness of God in all areas of their life, they will find a way to do it, too. And while these are all personal questions, it is applicable for everyone who professes to be Christian.

For this reason, I recognize it might be difficult for everyone to discern true Christians from false Christians (who should not be confused with non-Christians such as atheists), because it depends on their degree of maturity. The attributes and outward actions that would disqualify you as a true Christian is the unashamed practice of sin, where repentance is clearly not important or applicable. There is a big difference between those who desire to live like Christ and wage war on sin and crucify the flesh versus those who claim to live like Christ but embrace a fleshly life of sin c’est la vie and do not struggle with it at all; or worse, they hide it completely from the congregation and desire to take advantage of the weaker faith (2 Peter 2). In other words, there is self-deception and false teachers in the Church at large. Both of which we should be mindful of.

Sorry for the long response, Dean. It’s a really big question. I hope it helps–––God bless!