In reality, crossing the line refers to many negative actions and doings that are very hard to overcome if done. In Christianity, Crossing the Line means going to the other side, where the prosperity is.
There will be Spiritual Wars, but the reward is better than the life on the old side. A New Life and Perspective is change for us.
Just like how the Israelites led by both Moses and Joshua crossed the Red Sea and the Jordan River respectively, they could not go back. Same as us, we cannot go back after crossing the line to follow God.
The Israelites complained after crossing in Exodus 3:16, wanting to go back to Slavery. That's what happens when we go back to our Old Self.
Ultimately, in order to even have Change, we need to have Faith in God and his Plans.
Have a New LIfe, New Perspective, a Changed Life for God.