How can the prodigal son come back when it is supposed to be impossible for the fallen to come back?

Answer:

"For it is impossible for those who were once enlightened, and have tasted the heavenly gift, and have become partakers of the Holy Spirit, and have tasted the good word of God and the powers of the age to come, if they fall away, to renew them again to repentance, since they crucify again for themselves the Son of God, and put Him to an open shame" (Hebrews 6:4-6).

Satan whispers in many people's ears, "See, God has rejected you. He doesn't want you back." But it is a twisting of what this passage says.

Who is this verse written about? It is talking about people who once had salvation but decided to throw it away for cheap, temporary, worldly thrills.

Who is this verse written to? Is it written to the person who fell away or to those who try to bring them back? Read it carefully. It is written to people who long for the sinner's return. God is telling the faithful that they can't make the sinner come back. The faithful have little to offer the sinner that the sinner doesn't already know. The faithful can remind the sinner of the truth, but they can't tell the fallen something new that will suddenly make him realize to the depth of his soul that he needs to return. It is impossible for faithful to bring the fallen to renewal.

In the story of the prodigal son, his father longed for his return. I'm sure he didn't want him to leave and he knew his son was making a huge mistake. Yet, it wasn't until the son realized he needed to return that the son returned.

When someone has never heard the truth, I can teach him and he might change his ways to follow after the Lord. But if someone already knows the truth and decides to return to sin, there isn't something new I can teach him to make him realize the error of his ways. I can talk to him. I can encourage him. But the reality is that he must realize that he needs to come back.