When I was a brand-new Christian, I had a great burden to share the gospel exclusively with really cute girls. I thought, Why would I want to talk to just anyone? I'll talk to cute girls. They need the Lord, too.
But God got my attention, and I changed my way of thinking.
The problem with being involved with a nonbeliever is that most often, a nonbeliever will pull a Christian down spiritually—not the other way around. There are exceptions. But generally that is the case. It is miserable, and it is not God's plan for a believer.
We see this played out in the life of Samson, whom God raised up to be a leader over Israel. Apparently Samson didn't care much about what God's plan was, because he got involved with an unbelieving woman. One thing led to another, and things escalated. The Devil caught the mighty Samson hook, line, and sinker.
Samson's problem was that he had power without purity and strength without self-control. For twenty years, Samson experienced the thrill of victory. Not once had he been defeated. He should have been so thankful to God. We could say that God gave Samson a lot of rope, and Samson ended up hanging himself.
Any step away from God is always a step down. After God told Jonah to go to Nineveh, the Bible says that "Jonah arose to flee to Tarshish from the presence of the LORD. He went down to Joppa, and found a ship going to Tarshish; so he paid the fare, and went down into it, to go with them to Tarshish from the presence of the Lord" (Jonah 1:3).
When you are going away from God, you are always going down—never up.