Sheep don’t run away unless there is danger. However, if there is no shepherd, they will wonder, stray or drift away. The Bible refers to Jesus as the good Shepherd and his followers as sheep.
The book of Judges illustrates the way Israel acted like sheep. After Ehud was dead, the Israelites again did evil in the site of the Lord. They did not immediately, on the day of Ehud’s death, run away from the Lord and return to wickedness. Rather it was a process of drifting or sliding away from what was righteous into unrighteousness. Ehud had been the shepherd. As long as he lived and was there to guide them correctly, they were content to follow his leadership. However, their righteousness was limited to their right relationship with an earthly leader. They did not have an active ongoing relationship with God, and they did not have a personal commitment to doing what was right no matter what the price.
When their earthly leadership was taken away, they did not have an internal moral compass to follow and they did not have the Holy Spirit as an internal presence to guide them in righteous living. There was not a lack of faith, but rather a lack of faithfulness. They knew what was right, but without external leadership to keep them centered, they drifted into wickedness. The nature of sin is such that the more a person moves in its direction, the stronger its pull becomes upon the person.
God wants us to have a personal relationship with him. He has given us the Holy Spirit to make that relationship possible. Like any relationship, a relationship with God requires time and effort. If we are willing to make the effort, we can build an active, son or daughter relationship with God. Some Christians are content to remain sheep, they follow the closest Shepherd. If they lose their earthly leadership they risk drifting away. If we insist upon behaving like sheep following a shepherd, that Shepherd must be Jesus.