Numbers 15:35

5. “The Son of man,” he says, “is Lord of the Sabbath, and in that day it is by all means lawful to do good rather than do evil.” If, therefore, we do evil when we break our fast, there is no Lord’s day upon which we live as we should. As to his admission that the apostles did eat upon the seventh day of the week, and his remark upon this, that the time for their fasting had not then come, because of the Lord’s own words, “The days will come when the Bridegroom shall be taken away from them, and then shall the children of the Bridegroom fast;” since there is “a time to rejoice, and a time to mourn,” he ought first to have observed, that our Lord was speaking there of fasting in general, but not of fasting upon the seventh day. …

5. Since you hold to the divine authorship of the Old as well as of the New Testament, it would surely be more consistent and more becoming, as you do not obey its precepts, to confess that it has been corrupted by improper additions, than to treat it so contemptuously, if it is genuine and uncorrupted. Accordingly, my explanation of your neglect of the requirements of the Old Testament has always been, and still is, that you are either wise enough to reject them as spurious, or that you have the boldness and irreverence to disregard them if they are true. At any rate, when you would oblige me to believe everything contained in the documents of the New Testament because I receive the Testament itself, you should consider that, though you profess to receive the Old Testament, you in your heart disbelieve many things in it. …

Wherefore then was he punished that was gathering the sticks? Because if the laws were to be despised even at the beginning, of course they would scarcely be observed afterwards.

The seventh day is called the Sabbath and signifies rest. For in it God rested from all His works, as the divine Scripture says: and so the number of the days goes up to seven and then circles back again and begins at the first. This is the precious number with the Jews, God having ordained that it should be held in honour, and that in no chance fashion but with the imposition of most heavy penalties for the transgression. And it was not in a simple fashion that He ordained this, but for certain reasons understood mystically by the spiritual and clear-sighted.