You will find an emphasis on true and false teaching in 1 John. It has has always been a mark of the true church to distinguish between what is true and false. John points to errors about the nature of Jesus, the nature of sin, the role of sanctification in the life of a Christian and more. No teaching of Scripture is unimportant. If God has given it, it is for our good, and we are called to defend it and proclaim it faithfully. Our summary verse is from 1 John 4:1: “Dear friends, do not believe every spirit, but test the spirits to see if they are from God, because many false prophets have gone out into the world.” – (CSB)

source https://burdenblessing.podbean.com/e/63-1-john-summary-verse/