God testified of His Son’s identity as God at His baptism, at His crucifixion, and by the miraculous works of the Holy Spirit. We must not reject His testimony but accept it and embrace Jesus as Lord.
All who are born of God trust in Christ, love God and His people, and keep His commandments. These are the undeniable marks of regeneration: faith, love, and obedience.
God’s love has reached its goal (perfected) in us when we love one another. This is what boosts our confidence that we are indeed the children of God who by the Holy Spirit have Christ in us, who Himself loved God’s people as God loves them.
Truth and love go hand in hand. The truth of the gospel is what fuels Christian love. The love of God demonstrated in the coming of the Savior is what binds believers to love one another and provides the full resources to do so.
The Spirit leaves an indelible mark on those who belong to His truth. They love the people of God and they keep the commandments of God. These are the evidences of genuine faith which John points out for our assurance.