Keeping His Sabbaths and reverencing His sanctuary in this context seems to imply very strongly what God had in mind when He inspired those comments forbidding the observing of times. To me, considering Paul's reverence for the Old Testament, he certainly did not have so-called "Jewish days" in mind at all. He had pagan practices in mind. Galatians 4:10 cannot be used to affirm that one is not to observe God's Sabbath and holy days.