Ezequiel 9:4

Set a mark upon the foreheads. — The word for mark is literally a Tau, the last letter of the Hebrew alphabet. This, in many of the ancient alphabets, and especially in that in use among the Hebrews up to this time, and long retained upon their coins, was in the form of a cross — X or +. Much stress was laid upon this use of the sign of the cross as the mark for the Divine mercy by the older Christian writers, Tertullian, Origen, Cyprian, and Jerome. This marking was done, it is true, in vision, but the symbolism is taken from such passages as Gênesis 4:15; Êxodo 12:7; Êxodo 12:13; Êxodo 28:36; and it is used several times in the Apocalypse (Ezequiel 7:3; Ezequiel 9:4; Ezequiel 14:1). Such marks may be necessary for the guidance of the angelic executors of God’s commands, and at all events, the symbolism is of value to the human mind. It is with reference to such Scriptural instances of marking, doubtless, that the Church has provided for the signing of the baptized with the sign of the cross. It is to be observed here that the distinction of the marking has reference wholly and only to character. No regard is paid to birth or position; they and they only are marked who mourned for the prevailing sinfulness, and kept themselves apart from it.