John writes to help believers know they have eternal life. Three tests run through the letter: do you walk in the light, love one another, and confess that Jesus is the Christ come in the flesh? Where these are present, assurance follows.
“If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.”
“Behold, what manner of love the Father hath bestowed upon us, that we should be called the sons of God.”
“He that loveth not knoweth not God; for God is love.”
“We love him, because he first loved us.”