We do not know why Peter decided to go fishing, but if it was that he had gone back to his old way of life, we can learn a lot from it.
1.) If Peter had taken his eyes off of Jesus, he led others astray with him. A lot of the times our decisions affect those around us and do more harm than we realize.
2.) If they were backsliding, they did not recognize Jesus on the shore bc they had taken their eyes off of him and lost faith. We so easily forget the gospel and constantly need to be reminded.
3.) The disciples caught nothing after fishing all night so Jesus had to remind them of who He is and that apart from him, we can do nothing.
4.) Because of love we see Jesus and of course, the one whom Jesus loved and the one who stood beside Jesus through it all was the first to realize that it was their Lord that had guided them that morning.