“Since you have purified your souls in obeying the truth through the Spirit in sincere love of the brethren, love one another fervently with a pure heart.”
with a pure heart
The word “pure” means genuine, not hypocritical (Romans 12:9).
The word “heart” is an important biblical term,
“Hear, O Israel: The Lord our God, the Lord is one! You shall love the Lord your God with all your heart, with all your soul, and with all your strength” (Deuteronomy 6:4).
God wants us to love with all our might. This is the biblical standard of love.
If we are not consistent in love for the brethren, our behavior will betray our profession. Neglecting to love the brethren shows we are still spiritually dead (1 John 3:14) and that we have not come into a genuine relationship with God (1 John 4:8).
“With a pure heart” can be translated as “out of a pure heart.” We love others because of our regeneration. We have a natural love for the people of God because we have been purified (forgiven) from our sins. Pure love comes from a pure heart.
Purify means to remove foreign elements (Acts 21:23-27). Lay aside evil, put off lust, hatred, envy, and hypocrisy (James 4:8; 1 John 3:2-3).
Personal purity produces pure love.
A “pure heart” is a heart in full fellowship with God. A wife wants the whole heart of her husband. God wants us to love from the heart.