After a while Paul said to Barnabus, "Let's go back and visit our fellow Christians in every town where we told them the Lord's Word, and let's see how they are."
Barnabus wanted to take along John, who was called Mark. But Paul thought it best not to take the man who had deserted them in Pamphylia and had not gone with them into the work. They disagreed so sharply that they separated, and Barnabus, taking Mark along, sailed away to Cyprus. But Paul chose Silas and started out, his fellow Christians entrusting him to the Lord's grace.
There are many lessons that could be drawn from this lesson, and there are some debates as to who was in the right. In the end, I don't feel that it truly matters for us who was in the right, as we can learn lessons from both Paul and Barnabus.
For Paul, he saw this guy who was, at least as he perceived, unfaithful. He had let them down before, he very well might let them down again. Paul hadn't really seen him since he abandoned them in Pamphylia, and he didn't know if Mark's heart had changed, or if he he might run away at the first sign of trouble. Or maybe he was just having a hard time forgiving Mark for running away. Maybe it was both.
Barnabus, on the other hand, was ready to give Mark a second chance. Maybe he felt there were extenuating circumstances for why Mark had left them. Perhaps he was just moved to forgive Mark.
The bottom line is, here were these two great men of God, and they were split up by a disagreement. In other words, even among Christians, fights happen. They can be seemingly unavoidable. But what is truly important is what you do after a fight. Although they separated, Paul and Barnabus did not let this stop them from serving God. They didn't let this take them out. They kept on serving God. That is the single most important thing that you can take away from this lesson: whatever does happen, never stop serving God.
Despite any trial that might cross your path, no matter how bad it hurts, never walk away from Jesus. He knows how it is to be betrayed. He knows how it is to be hurt by someone you love. He knows how it hurts when someone walks away from you. Keep your eyes focused on Him, and things are gonna work out.
"Only Luke is with me. Get Mark and bring him with you, because he's a good help to me in my work." 2 Timothy 4:11
In the end, Paul knew that Barnabus did the right thing by giving Mark a second chance. Be open to the fact that maybe you could be in the wrong in the next disagreement that you have with someone.