Don’t be confused:
1 John (pronounced “First John” is the 23rd book of the New Testament) is different from the Gospel of John (the 4th book of the New Testament). They both were written by the apostle John. The primary purpose of the Gospel of John (the 4th book) is to help the Church trust that Jesus is the anointed one and the Son of God, and that by trusting in Him, we will have eternal life by His authority.
But on the other hand, the purpose of 1 John is to bring confidence and power and light and truth and God’s kind of love to the local church body (REVIVAL!).