RobH_en_tn/1jn/03/20.md

if our hearts condemn us

Here "hearts" is a metonym for people's thoughts or consciences. Here "hearts condemn us" is a metaphor for feeling guilty. Alternate translation: "if we know that we have sinned and as a result feel guilty" (See: rc://en/ta/man/translate/figs-metonymy and rc://en/ta/man/translate/figs-metaphor)

God is greater than our hearts

Here "hearts" is metonym for people's thoughts or consciences. For God to be "greater than our hearts" means that God knows more than a person. Therefore he can judge things better than a person can. The effect of this truth is probably that God is more merciful than our consciences would suppose. Alternate translation: "God knows more than we do" (See: rc://en/ta/man/translate/figs-metonymy)