19 Some from the tribe of Manasseh also defected to David when he started out with the Philistines to go to war against Saul. In the end, they didn't actually fight because the Philistine leaders, after talking it over, sent them home, saying, "We can't trust them with our lives - they'll betray us to their master Saul."
Matthew Henry's Commentary on 1 Chronicles 12:19
Commentary on 1 Chronicles 12:1-22
(Read 1 Chronicles 12:1-22)
Here is an account of those who appeared and acted as David's friends, while he was persecuted. No difficulties or dangers should keep the sinner from coming to the Savior, nor drive the believer from the path of duty. Those who break through, and overcome in these attempts, will find abundant recompence. From the words of Amasai we may learn how to testify our affection and allegiance to the Lord Jesus; his we must be throughly; on his side we must be forward to appear and act. If we are under the influence of the Spirit, we shall desire to have our lot among them, and to declare ourselves on their side; if in faith and love we embrace the cause of Christ, he will receive, employ, and advance us.