1 John 3:11-12, 23

For this is the message which you have heard from the beginning, that we should love one another; not as Cain, who was of the evil one and slew his brother. And for what reason did he slay him? Because his deeds were evil, and his brother’s were righteous.

This is His commandment, that we believe in the name of His Son Jesus Christ, and love one another, just as He commanded us.