What does Galatians 4:10 mean?

The Galatian Christians had initially responded to Paul's message of salvation by grace, though faith (Galatians 1:6). However, a certain group, known as the Judaizers, had begun to claim that salvation also required adherence to the law of Moses (Galatians 2:4). Paul has been pointing out how "foolish" it is for the Galatians to turn from a gospel of faith, to a gospel of works.

Paul now points to some specific works of the law that these Galatian Christians have begun to follow. They have started to observe specific "days and months and seasons and years." He means that they have started to observe and celebrate all the special days and holidays Israel was commanded to observe under the law of Moses. These days would have included the weekly Sabbath with all of its restrictions, beginning Friday at sunset and lasting until Saturday at sunset. It would have included specific festivals and fasts and days of remembrance. From the time of Moses until the time of Christ, all Israelites were required to obey God by observing these days. Failing to observe them was reason enough for God to remove His blessing under His covenant with Israel.

Is Paul saying that it is always wrong for believers to observe any special "holy days"? Not necessarily, but one does need to be aware of motives. In Romans 14, Paul describes those kinds of actions as a matter of conscience: "One person esteems one day as better than another, while another esteems all days alike. Each one should be fully convinced in his own mind. The one who observes the day, observes it in honor of the Lord" (Romans 14:5–6).

The problem was that these Christians were observing all the special days, not to honor the Lord, but to be honored by Him. They hoped to be more fully justified and holy as followers of Christ. They believed this because they were listening to the group of false teachers known as the Judaizers.

In doing so, the Galatian Christians showed they were not convinced God had already fully justified them by their faith in Christ. They were making themselves slaves to sin again by expecting God to approve of their works instead of simply accepting them, in love and by His grace, as His children in and through Christ.