John Lightfoot on Matthew 23:5

[They make broad their phylacteries.] These four places of the law, Exodus 13:3-10, Exodus 13:11-16, Deuteronomy 6:5-9, Deuteronomy 11:13-21; being writ upon two parchment labels (which they called tephillin), were carried about with them constantly with great devotion, being fastened to their forehead and their left arm. To the forehead, in that place where the pulse of an infant's brain is. This of the forehead was most conspicuous, and made broad: hence came that, "Let nobody pass by the synagogue while prayers are saying there.--But if he hath phylacteries upon his head, he may pass by, because they show that he is studious of the law."--"It is not lawful to walk through burying-places with phylacteries on one's head, and the book of the law hanging at one's arm."

They are called in Greek phylacteries, that is, observatories; because they were to put them in mind of the law; and perhaps they were also called preservatories, because they were supposed to have some virtue in them to drive away devils: "It is necessary that the phylacteries should be repeated at home a-nights, to drive away devils."

Concerning the curious writing of the phylacteries, see Maimonides on Tephellin. Concerning their strings, marked with certain small letters, see Tosaphoth on Megillah. Concerning the repeating of them, see both the Talmuds in Beracoth. How the Jews did swear touching their phylacteries, see Maimonides in Shevuoth: and how God is brought in swearing by the phylacteries, see Tanchum.

Our Saviour does not so much condemn the bare wearing of them, as the doing it out of pride and hypocrisy. It is not unlikely that he wore them himself, according to the custom of the country: for the children of the Jews were to be brought up from their infancy in saying the phylacteries; that is, as soon as they were capable of being catechised. The scribes and Pharisees made theirs very broad and visible, that they might obtain a proportional fame and esteem for their devotion with the people; these things being looked upon as arguments of the study of the law, and signs of devotion.

[Enlarge the borders of their garments.] See Numbers 15:38; Deuteronomy 22:12--"He that takes care of the candle of the sabbath, his children shall be the disciples of wise men. He that takes care to stick up labels against the posts shall obtain a glorious house; and he that takes care of making borders to his garment, shall obtain a good coat."