This is a disturbing thing for Paul to say, and is intended to shake them in their complacency. If Paul was afraid for them, how much more should they be afraid for themselves? It ought to have deeply troubled them that the one who had been used to bring them to Christ should now question the reality of their conversion.
For the sake of all those who will have to wrestle with similar problems as pastors of God’s churches, Paul shows how these things should be handled and something of the heartache of being a pastor for which every man called by God must prepare. It is right at times for a minister of God to have doubts about a backsliding church, for he must be a realist in assessing by God’s help the spiritual state and needs of all those he ministers to, for he watches for their souls as one that must give account to God (Hebrews 13:17). It is not always his role to comfort, but at times he must warn and even be responsible for causing great turmoil in another heart. This turmoil, if it leads to repentance, is better than the dreadful realisation on the day of judgment that a person has fallen short of grace. The Galatians had abandoned their trust in Christ alone; doctrinal departure is very dangerous. The Bible never takes the approach that as long as a man lives uprightly, it doesn’t matter what he believes, for works that do not come from faith are dead.