Albert Barnes' Notes on the Whole Bible - Matthew 5:36
Neither shalt thou swear by thy head - This was a common oath. The Gentiles also used this oath. To swear by the head was the same as to swear by the life; or to say, I will forfeit my life if what I say is not true. God is the Author of the life, and to swear by that, therefore, is the same as to swear by him.Because thou canst not make one hair white or black - You have no control or right over your own life. You cannot even change one single hair. God has all that control; and it is... read more
The Pulpit Commentary - Matthew 5:36
For thou canst not , etc. As each of the other objects included a reference to God, so does also thy head. For even that recalls to mind the power of God, since every hair of it bears the stamp of his handiwork. read more