1 John 2:5 (ESV) … “but whoever keeps his word, in him truly the love of God is perfected. By this we may know that we are in him…”
The more we obey God’s Word, the more we open the door for his love to accomplish his purpose in our lives. The test of living in the light is growing in love for God. And the ultimate proof of that is not in the heightened emotion of exciting worship (though that may well be an expression of reality) but in the daily, detailed, disciplined obedience by which our characters are being transformed into the image of the God we love. Nor is that ‘word’ simply one of imperative command, for wherever commands occur in Scripture they are surrounded by promises, which lead us to a deeper awareness of God’s love for us and a deeper reciprocation in our love for him, as we trust and obey.
The ‘complete’ love of which verse 5 speaks is simply meant to underline for us the fact that obedience is the way to growth and maturity. ’John is here speaking, as often in this Epistle, of an ideal state of things. No Christian’s love to God is perfect; but the more perfect his knowledge, the more perfect his obedience and his love.
The section ends with a renewed emphasis on our practical walk in everyday life. How did Jesus walk? Certainly in the light with God, due to his perfect obedience to the heavenly Father’s will, to which God himself testified (Mt. 3:17; 12:18; 17:5). But he also walked in love towards the crowds of needy, lost people whom he daily encountered (Mt. 9:36). Walking in the light is not only characterized by the absence of sin but equally importantly by the presence of love. Those who remain (abide) in Christ cannot fail to display the fruit of the Spirit, in a Christ-like character.
Just as the life flowing through the vine enables the branches to bear fruit, and that fruit indicates the nature of the plant’s life within, so it is with a true Christian who abides in Christ (see Jn. 15:1–8). ‘By their fruit you will recognise them. Do people pick grapes from thornbushes, or figs from thistles?’ (Mt. 7:16). If we really walk in the light with God, our behaviour will become more and more like that of the Lord Jesus. It is not that we obey God’s commands in order to make ourselves good enough to walk in the light with him. That is the cul-de-sac called legalism. Rather, those who truly walk with God love to obey him, because in that way they grow a little more like him each day. That is the high road called grace.
 Jackman, D. (1988). The message of John’s letters: living in the love of God (pp. 49–50). Leicester, England; Downer’s Grove, IL: InterVarsity Press.