Substantial part of the answer to the 'riddle' the Sabbath has become for most Christians, is the "SUBSTANCE-day" of the "three days" of Christ's Last Suffering which He so 'passionately' spoke about.
Jesus spoke with and without 'parables' concerning the "three days" of "the plague [that] was upon Him". For these "three days" were the "THREE DAYS THICK DARKNESS" of the last two of Egypt's ten plagues indeed that ended in Israel's exodus from the land of Egypt and entrance into the promised land.
Due to THIS redemption of the People of God the 'creation-motive' was completely dropped and was replaced with REDEMPTION in the Fourth Commandment as reason for the Sabbath.
The middle-day of the "three days" received central importance in the Scriptures for 'the God-given and therefore eschatologic imperative whole and wholeness' (using Lohmeyer's terminology) thereof and which its very name, "BONE-DAY", is indicative of.
Once exposed, "Bone-Day" changes perspective, approach, conception and expression of contemplation, discussion and conclusion about the usual and traditional understanding of Jesus Christ's Last Passover. And inevitably about the Sabbath for the Christian Faith.
UNDERSTANDING THE SCRIPTURES NEVER WILL BE THE SAME AGAIN.