Evidence of a Christian life is the fruit we bear. That isn’t an option but a given. A Christian bears fruit.
Matt 3:8 (ESV) Bear fruit in keeping with repentance.
Everyone bears fruit, that isn’t the question. But as believers we should bear fruit for life, for God, for righteousness and the fruit of light.
Rom 7:4-6 (ESV)
4 Likewise, my brothers, you also have died to the law through the body of Christ, so that you may to another, to him who has been raised from the dead, in order that we may bear fruit for God. 5 For while we were living in the flesh, our sinful passions, aroused by the law, were at work in our members to bear fruit for death. 6 But now we are released from the law, having died to that which held us captive, so that we serve not under the old written code but in the new life of the Spirit.
Phil 1:9-11 (ESV)
9 And it is my prayer that your love may abound more and more, with knowledge and all discernment, 10 so that you may approve what is excellent, and so be pure and blameless for the day of Christ, 11 filled with the fruit of righteousness that comes through Jesus Christ, to the glory and praise of God.
Eph 5:7-12 (ESV)
7 Therefore do not associate with them; 8 for at one time you were darkness, but now you are light in the Lord. Walk as children of light 9 (for the fruit of light is found in all that is good and right and true), 10 and try to discern what is pleasing to the Lord. 11 Take no part in the unfruitful works of darkness, but instead expose them.
Rom 6:20-23 (ESV)
20 When you were slaves of sin, you were free in regard to righteousness. 21 But what fruit were you getting at that time from the things of which you are now ashamed? The end of those things is death. 22 But now that you have been set free from sin and have become slaves of God, the fruit you get leads to sanctification and its end, eternal life. 23 For the wages of sin is death, but the free gift of God is eternal life in Christ Jesus our Lord.
According to Galatians 5 there are some other fruits all Christians should bear.
Gal 5:22-23 (ESV) 22 But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, 23 gentleness, self-control; against such things there is no law.
No option is given. All Christians should bear the following fruits for God:
Believe me, as a parent, teaching children to bear those fruits can be difficult and encompass all your time, partly because we as parents are still learning to bear the same fruits.
Sometimes the Lord blesses us with children who have fewer struggles bearing some of the fruit than others do. There are babies who are born who naturally are more loving and more joyful while another child in the same family may struggle with being loving and joyful. That doesn’t mean that we as parents can allow that struggling child to get by with less because they display that sin nature more so than another. We, and they, might have to work harder to produce fruit. But the fruit will be more cherished when it comes because it required such hard work.
There may be a long time before a child bears fruit on their own. Just as we don’t expect a real fruit tree to bear an abundance of fruit the first year we plant it. However, there is a lot we as parents can do to help encourage our children to bear good and lasting fruit. Just as we would water, fertilize and train a tree, we are doing similar for our children. Those trees that do not eventually bear good and lasting fruit will be cut down and thrown into the fire.
Matt 3:10 (ESV) Even now the axe is laid to the root of the trees. Every tree therefore that does not bear good fruit is cut down and thrown into the fire.
While we as parents can only encourage, disciple and train our children to bear righteous fruit, it is the Holy Spirit who will enable our children to bear true Christian fruit. Prayerfully at some point the Holy Spirit will come along side and convict and guide our children, taking over for us, as they strive to bear fruit in keeping with righteousness. If your older child who claims to be a Christian is not showing fruit or at least showing buds of fruit you may need to question them and have them consider if they are truly a Christian.