John’s Gospel showed us that life as only Jesus can give us, life abundant and eternal, can only be received. Jesus was and is the Word of Life, and He was revealed by the Father to be the giver of life to those who would come to Him with the empty hands of faith. John’s aim in his Gospel was that people might see His works and hear His words and believe that He is the Christ, the Son of God, and by faith have life.
John’s first letter is what the Gospel of John looks like applied to a local church. John begins his letter much the way he ended his Gospel, but he now has a “so that” attached. Once one has believed and received life, what’s next? What is the goal?