NET
5 But whoever obeys his word, truly in this person the love of God has been perfected. By this we know that we are in him.
Darby
5 but whoever keeps his word, in him verily the love of God is perfected. Hereby we know that we are in him.
KJV
5 But whoso keepeth his word, in him verily is the love of God perfected: hereby know we that we are in him.