From: Mark 2:23-28
The Law of the Sabbath
 One Sabbath He (Jesus) was going through the grainfields; and as they made their way His disciples began to pluck ears of grain.  And the Pharisees said to Him, "Look, why are they doing what is not lawful on the Sabbath?"  And He said to them, "Have you never read what David did, when he was in need and hungry, he and those whowere with him:  how he entered the house of God, when Abiathar was high priest, and ate the bread of the Presence, which it is not lawful for any but the priests to eat, and also gave it to those who were with him?"  And He said to them, "The Sabbath was made for man, not man for the Sabbath;  so the Son of Man is Lord even of the Sabbath."
24. Cf. note on Matthew 12:2. [Note on Matthew 12:2 states: "The Sabbath": this was the day the Jews set aside for worshipping God. God Himself, the originator of the Sabbath (Genesis 2:3), ordered the Jewish people to avoid certain kinds of work on this day (Exodus 20:8-11; 21:13; Deuteronomy 5:14) to leave them free to give more time to God. As time went by, the rabbis complicated this Divine precept: by Jesus' time they had extended to 39 the list of kinds of forbidden work.
The Pharisees accuse Jesus' disciples of breaking the Sabbath. In the casuistry of the scribes and the Pharisees, plucking ears of corn was the same as harvesting, and crushing them was the same as milling--types of agricultural work forbidden on the Sabbath.]
26-27. The bread of the Presence consisted of twelve loaves or cakes placed each morning on the table in the sanctuary, as homage to the Lord from the twelve tribes of Israel (cf. Leviticus 24:5-9). The loaves withdrawn to make room for the fresh ones were reserved to the priests.
Abiathar's action anticipates what Christ teaches here. Already in the Old Testament God had established a hierarchy in the precepts of the Law so that the lesser ones yielded to the main ones.
This explains why a ceremonial precept (such as the one we are discussing) should yield before a precept of the natural law. Similarly, the commandment to keep the Sabbath does not come before the duty to seek basic subsistence. Vatican II uses this passage of the Gospel to underline the value of the human person over and above economic and social development: "The social order and its development must constantly yield to the good of the person, since the order of things must be subordinate to the order of persons and not the other way around, as the Lord suggested when He said that the Sabbath was made for man and not man for the Sabbath. The social order requires constant improvement: it must be founded on truth, built on justice, and enlivened by love" ("Gaudium Et Spes", 26).
Finally in this passage Christ teaches God's purpose in instituting the Sabbath: God established it for man's good, to help him rest and devote himself to Divine worship in joy and peace. The Pharisees, through their interpretation of the Law, had turned this day into a source of anguish and scruple due to all the various prescriptions and prohibitions they introduced.
By proclaiming Himself `Lord of the Sabbath', Jesus affirms His divinity and His universal authority. Because He is Lord He has the power to establish other laws, as Yahweh had in the Old Testament.
28. The Sabbath had been established not only for man's rest but also to give glory to God: that is the correct meaning of the _expression "the Sabbath was made for man." Jesus has every right to say He is Lord of the Sabbath, because He is God. Christ restores to the weekly day of rest its full, religious meaning: it is not just a matter of fulfilling a number of legal precepts or of concern for physical well-being: the Sabbath belongs to God; it is one way, suited to human nature, of rendering glory and honor to the Almighty. The Church, from the time of the Apostles onwards, transferred the observance of this precept to the following day, Sunday--the Lord's Day--in celebration of the resurrection of Christ.
"Son of Man": the origin of the messianic meaning of this _expression is to be found particularly in the prophecy of Daniel 7:13ff, where Daniel, in a prophetic vision, contemplates `one like the Son of Man' coming down on the clouds of Heaven, who even goes right up to God's throne and is given dominion and glory and royal power over all peoples and nations. This _expression appears 69 times in the Synoptic Gospels; Jesus prefers it to other ways of describing the Messiah--such as Son of David, Messiah, etc.--thereby avoiding the nationalistic overtones those expressions had in Jewish minds at the time (cf. "Introduction to the Gospel according to St. Mark", p. 62 above).
Source: "The Navarre Bible: Text and Commentaries". Biblical text taken from the Revised Standard Version and New Vulgate. Commentaries made by members of the Faculty of Theology of the University of Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock, Co. Dublin, Ireland. Reprinted with permission from Four Courts Press and Scepter Publishers, the U.S. publisher.