John Chrysostom

But Mark declares that He uttered this of our common nature, for He said, The sabbath was made for man, not, man for the sabbath. It is therefore more fitting that the sabbath should be subject to man, than that man should bow his neck to the sabbath.

Catena Aurea by Aquinas ↗

Theophylact of Ohrid

But he reproves them in another way, as it is added, And he said unto them, that the So of man is Lord also of the sabbath. As if he said, I am the Lord of the sabbath, as being He who ordained it, and as the Legislator I have power to loose the sabbath; for Christ was called the Son of man, who being the Son of God yet condescended in a miraculous manner to be made and called for man's sake the Son of man.

Catena Aurea by Aquinas ↗

Bede

And he said to them, because the Son of Man is also Lord of the Sabbath. If, he said, King David who was fed with priestly food is excusable, and according to the faith of another Gospel, the priests violating the Sabbath through temple service are without crime, how much more the Son of Man, who is the true King and true Priest, and therefore the Lord of the Sabbath, is not held liable for the offense of plucking ears of grain on the Sabbath.

On the Gospel of Luke ↗

Bonaventure

And lest anything be lacking to the authority of Scripture, he subjoins his own authority, by which he both willed and was able to grant them a dispensation. Which he indicates when he adds: And he said to them, that the Son of man is Lord also of the Sabbath. …

Commentary on Luke, Chapter 6 ↗