"And it came to pass on the second sabbath after the first, that he went through the corn fields; and his disciples plucked the ears of corn, and did eat, rubbing them in their hands. And certain of the Pharisees said unto them, Why do ye that which is not lawful to do on the sabbath days?" (Luke 6:1-2)

The initial purpose of the sabbath was to give man rest so that he could work the other six days of the week. This basic meaning and purpose must not be overlooked.

We first see the idea presented very early in the Bible in the book of Genesis.

"Thus the heavens and the earth were finished, and all the host of them. And on the seventh day God ended his work which he had made; and he rested on the seventh day from all his work which he had made. And God blessed the seventh day, and sanctified it: because that in it he had rested from all his work which God created and made."(Genesis 2:1-3)

We know that Jesus declares that his Father and He are still working but the idea is that God rested from a particular work. In this case, creation.

"Remember the sabbath day, to keep it holy. Six days shalt thou labour, and do all thy work: but the seventh day is the sabbath of the Lord thy God: in it thou shalt not do any work, thou, nor thy son, nor thy daughter, thy manservant, nor thy maidservant, nor thy cattle, nor thy stranger that is within thy gates: for in six days the Lord made heaven and earth, the sea, and all that in them is, and rested the seventh day: wherefore the Lord blessed the sabbath day, and hallowed it."(Exodus 20:8-11)

But even before the law was given, the sabbath was observed as a day of rest, one day in every seven. In Exodus 16, it was observed by gathering a preparing enough manna for two days on the sixth day. The intent was to rest from servile work on the seventh.

We also find the concept of rest regarding fields for harvest in Leviticus 25. Here the land is worked for six years and allowed to rest for one. 

There are several other sabbath observances mentioned in the old law, but each time we see the word "sabbath" we find the common theme of rest. Man needs rest, therefore as Jesus said, God made the sabbath for man, not man for the sabbath. 

The Pharisees had corrupted the observance of sabbath days to the point of replacing the much needed rest with a stringent "no work" policy. This policy was so detailed and threatening that it gave no Liberty and therefore, no rest.