1 John 2:5 But whoso keepeth his word, in him verily is the love of God perfected: hereby know we that we are in him.
The love of God is in the one who believes in Jesus. Faith receives the love of God, and God’s Love grows and is being perfected in us. Faith produces love and good works in outward behavior. By looking at your life you may know you are in Him. “By their fruits you shall know them.”
The promise is that if we “keep his word” then the love of God is perfected in us. We do not focus our attention on the outward life of showing love and good works, but we focus on keeping his word. When we do so, the Love of God in us works through us to love others and act kindly toward them. This is the promise: repent and believe the gospel and the fruit will follow. Jesus promises in John 15:5: ”Whoever abides in me and I in him, he it is that bears much fruit, for apart from me you can do nothing (good, or loving).”
Keep the word = Abide in Jesus. Fruit (the love of God) will follow. We do not ”perfect the love.” He does. Our task is to hear the Law and repent, and to hear the Gospel and believe. When we focus our attention on Christ crucified then the love of God for us and toward others is perfected in us. Take that as a promise, and believe it. Thank God and give Him the glory!