8 Formerly, when you did not know God, you were slaves to those who by nature are not gods. 9 But now that you know God—or rather are known by God—how is it that you are turning back to those weak and miserable forces? Do you wish to be enslaved by them all over again? 10 You are observing special days and months and seasons and years! 11 I fear for you, that somehow I have wasted my efforts on you. (NIV)Christians have long debated whether or not it is appropriate to keep the sabbath. I'm not going to get into all of the intricacies of that debate, but I want to comment on how this passage fits into the wider discussion.
First, we should observe that the Gentile Galatians had already begun observing the sabbath. Why? They thought that they had to observe the Torah in order to be full members of God's people. Paul sees observing Torah, exemplified by, among other things, sabbath observance to be a step not into the people of God, but out of. A movement, not into the new creation, as part of the new covenant community of the faithful, but away from it. It puts them into a situation of slavery, one parallel to the situation that Christ already freed them from.
So, if that's the case, the next question is, should Paul's logic drive us to not keep the sabbath? I think that the answer is no. When we compare this text to Romans 14 we see a different approach by Paul to the question. There, he never flatly condemns sabbath observance. The weak are allowed to remain weak as long as it doesn't lead them to judge those who don't observe the sabbath. However, we do have to consider whether or not this difference in attitude lies in the fact that the weak in Rome were Jewish Christians. I think it does partially, but there's more to it. In Romans it's clear that the issue isn't really sabbath observance. It's all about attitude. Does your stance on the sabbath cause you to judge those you disagree with as lower class Christians? In Galatians I believe the issue is the same, just magnified, hence the heightened rhetoric. Do you believe that sans following the Torah you cannot be a full member of God's people? Sabbath observance is a visible work of the law that sets you apart from others. That is why Paul brings it, specifically, up. It's an easy target.
When it's cast like that I think it's clear that it can be ok to observe the sabbath. In fact I think most of us would be wise to have a regular time of rest and reflection on God. It would be (at least in my circles) a strong counter-cultural statement protesting against the societal god of productivity.