But whoever keeps his word, God's love has most assuredly been perfected in him. This is how we know that we are in him:
The love of God has been perfected ... Here is another glimpse of that absolute perfection which is the goal of all Christian living, mentioned by Jesus in  Matthew 5:48, and referred to by all the New Testament writers. Although unattainable by humans in their own strength, it will nevertheless be achieved in them and for them by means of their being "in Christ" and thereby partaking of the absolute perfection of the Saviour himself  (Colossians 1:28).  Significantly, the necessity of being "in him" is the concluding thought of this verse.