What does 1 John 4:21 mean?

This summarizing verse includes aspects from both verses 19 and 20. Believers must love God, and they must love other people. John specifically refers to this as a "commandment." Believers keep God's commandments (1 John 2:3). John mentioned other commandments in his letter, including loving one another (1 John 2:7–8) and believing in the name of Jesus (1 John 3:23). Here, love for God and others is included as a third commandment.

While this focus on commandments may seem difficult, 1 John 5:3 adds, "For this is the love of God, that we keep his commandments. And his commandments are not burdensome." In comparison to the laws of men as well as the many laws found in the Torah, Christ's commandments are few in number. However, His commandments are difficult in the sense that no one can perfectly love God and others. This is an ongoing goal that every believer must practice daily.