An alternate translation may help us to understand what Paul is getting at here: "These are a shadow of future things, but the reality [what is real or firm] belongs to Christ."
Old Testament activities or types point to spiritual realities under the New Covenant. He is not saying that Old Covenant activities no longer have to be observed, but rather that they need to be raised—elevated—to be understood and applied in their God-intended, spiritual sense.
Protestant scholars understand this fact, and they will even remark on it in their commentaries. Notice Conybeare and Howson's The Life and Epistles of St. Paul, page 346: "The festivals observed by the apostolic church were at the first the same with those of the Jews; and the observation of these was continued, especially by the Christians of Jewish birth, for a considerable time."
On page 574, they write: "Nay, more. He himself [Paul] observed the Jewish festivals." This clarifies that Colossians 2:16-17 is not telling us that the festivals—those so-called "Old Testament laws"—are done away. Rather, he is saying that they are to be raised, elevated, understood in a spiritual sense, rather than something that is merely material and physical.
Conybeare and Howson's conclusion is that, contrary to the common misunderstanding of these verses, the Bible and history show that the apostolic church kept God's holy days. Congregations dominated by Gentiles were the first to break away from them, as being too "Jewish," and begin to keep festivals like Christmas and Easter.
However, did keeping pagan festivals show forth the praises of God? The apostles clearly did not think so, or they would have kept them. It begins to become clear that Old Testament activities contain valuable instruction for the new covenant church.
John W. Ritenbaugh
New Covenant Priesthood (Part 1)