Jehovah said, Go through the midst of the city, through the midst of Jerusalem, and set a mark (that is, "mark out") upon the foreheads of the men groaning and sighing for all the abominations (Ezek. 9:4), where by "marking out the foreheads" is not meant a mark or line upon the front part of their heads, but to distinguish them from others. So in John, it is said that The locusts should hurt only those men who had not the mark of God on their foreheads (Rev. 9:4), where also to have the mark means to be distinguished. [2] And in the same book we read of a "mark on the hand and on the forehead" (Rev. 13:16). The same thing was represented in the Jewish Church by binding the first and great commandment on the hand and on the forehead, concerning which we read in Moses:

Hear, O Israel, Jehovah our God is one Jehovah; and thou shalt love Jehovah thy God with all thy heart, and with all thy soul, and with all thy strength, and thou shalt bind these words for a sign upon thy hand, and they shall be as frontlets between thine eyes (Deut. 6:4, 8; 11:13, 18). By this was represented that they should distinguish the commandment respecting love above every other, and hence the signification of "marking the hand and the forehead" becomes manifest. [3] So in Isaiah:

I come to gather all nations and tongues; and they shall come and shall see My glory; and I will set a mark upon them (Isa. 66:18-19). And in David:

O turn unto me, and have mercy upon me, give Thy strength unto Thy servant, and save the son of Thy handmaid. Set upon me a mark for good, and they that hate me shall see and be ashamed (Ps. 86:16-17).From these passages the meaning of a mark is now evident. Let no one therefore imagine that any mark was set upon a particular person called Cain, for the internal sense of the Word contains things quite different from those contained in the sense of the letter.