Charles Ellicott Commentary Ezekiel 9:4

"And Jehovah said unto him, Go through the midst of the city, through the midst of Jerusalem, and set a mark upon the foreheads of the men that sigh and that cry over all the abominations that are done in the midst thereof." — Ezekiel 9:4 (ASV)

Set a mark upon the foreheads. —The word for mark is literally a Tau, the last letter of the Hebrew alphabet. This letter, in many ancient alphabets, and especially in the one used by the Hebrews until that time and long retained on their coins, was in the form of a cross—X or +. Much stress was laid on this use of the sign of the cross as the mark for divine mercy by older Christian writers, such as Tertullian, Origen, Cyprian, and Jerome. This marking was done, it is true, in a vision, but the symbolism is taken from such passages as Genesis 4:15; Exodus 12:7; Exodus 12:13; Exodus 28:36; and it is used several times in the Apocalypse (Ezekiel 7:3; Ezekiel 9:4; Ezekiel 14:1).

Such marks may be necessary for the guidance of the angelic executors of God’s commands, and in any case, the symbolism is of value to the human mind. It is doubtless with reference to such scriptural instances of marking that the Church has provided for the signing of the baptized with the sign of the cross. It should be noted here that the distinction of the marking refers wholly and only to character. No regard is paid to birth or position; they, and only they, are marked who mourned for the prevailing sinfulness and kept themselves apart from it.