What does 1 John 5:13 mean?

Verse 13 directly states the overall purpose of John's letter, which is assuring true believers of their salvation. "These things" refers to the contents of the previous passage. Specifically, that belief in Christ guarantees salvation. A Christian does not need to guess whether he or she will have eternal life. Those who know God and love others show evidence God is in their life.

John has been specific regarding how a person can know they have eternal life. This starts with the only means of obtaining salvation, which is faith in the Son of God. There is no list of works a person can do to determine eternal life. Nor are there any sins a believer can commit which will cause them to lose it. Ultimately, eternal life is based—entirely—on whether a person has believed in Jesus Christ. Recognizing salvation, however, is a matter of examining one's life, for the kind of signs John has mentioned previously in this letter.

The eternal life John has spoken of so many times in this letter is of central importance, and it comes from one source: the Son of God. The remaining verses provide five additional teachings followed by a brief command to stay away from idols.