This letter attacks one of the most dangerous heresies, Gnosticism, which taught them and today that salvation was not achieved by belief in Jesus Christ, Son of God who rose from the dead in the flesh and returned to heaven, but by knowledge. The heresy was also libertine and the disregarding moral restraints. The text also assures believers of their salvation in Christ. The work lists the criteria, the characteristics of fellowship with God, and the basis of the fellowship. It exhorts believers to love one another, and love for God arises out of obedience.
Love is to be practiced in self-sacrifice.
The work is made up of brief statements of simple words. The word 'know' is used over thirty times to make an impact as does the word 'believe'. It brings Christians back to the basic truth. The First Book of John is the fourth of seven Church Letters. This universal work is also considered a Book containing teaching.