R. Zera said to R. Simeon, Let the Master rebuke the members of the Resh Galutha's suite. They will not accept it from me, was his reply. Though they will not accept its returned he, yet you should rebuke them. For R. Aha b. R. Hanina said: Never did a favourable word7 go forth from the mouth of the Holy One, blessed be He, of which He retracted for evil, save the following, where it is written, And the Lord said unto him, Go through the midst of the city, through the midst of Jerusalem, and set a mark [taw] upon the foreheads of the men that sigh and that cry for all the abominations that be done in the midst thereof, etc.8 The Holy One, blessed be He, said to Gabriel,9 Go and set a taw10 of ink upon the foreheads of the righteous, that the destroying angels may have no power over them; and a taw of blood upon the foreheads of the wicked, that the destroying angels may have power over them. Said the Attribute of Justice11 before the Holy One, blessed be He, 'Sovereign of the Universe! Wherein are these different from those?' 'Those are completely righteous men, while these are completely wicked,' replied He. 'Sovereign of the Universe!' it continued, 'they had the power to protest but did not.' 'It was fully known12 to them that had they protested they would not have heeded them.'13 'Sovereign of the Universe!' said he, 'If it was revealed to Thee, was it revealed to them?' Hence it is written, [Slay utterly] the old man, the young and the maiden, and little children and women; but come not near any man upon whom is the mark; and begin at my Sanctuary [mikdashi]. Then they began at the elders which were before the house.14 R. Joseph recited: Read not mikdashi but mekuddashay [my sanctified ones]: this refers to the people who fulfilled the Torah from alef to taw.15 And straightway, And behold, six men came from the way of the upper gate, which lieth toward the north, every man with his slaughter weapon in his hand; and one man in the midst of them clothed in linen, with a writer's inkhorn by his side. And they went in, and stood beside the brazen altar.16 Was then the brazen altar [still] in existence?17 — The Holy One, blessed be He, spake thus to them; Commence [destruction] from the place where song is uttered before Me.18 And who were the six men? — Said R. Hisda: Indignation [Kezef], Anger [Af], Wrath [Hemah], Destroyer [Mashhith] Breaker [Meshabber] and Annihilator [Mekaleh]. And why taw? — Said Rab: Taw [stands for] tihyeh [thou shalt live], taw [stands for] tamuth [thou shalt die]. Samuel said: The taw denotes, the merit of the Patriarchs is exhausted [tamah].19 R. Johanan said: The merit of the Patriarchs will confer grace [tahon].20 While Resh Lakish said: Taw is the end of the seal of the Holy One, blessed be He. For R. Hanina said: The seal of the Holy One, blessed be He, is emeth [truth]. R. Samuel b. Nahmani said: It denotes the people who fulfilled the Torah from alef to taw.21In a rather old parshablog post, I wrote the following:
Apropos Missisipi Fred Macdowell's question whether there is any value of non-academic types knowing Ktav Ivri (Paleo-Hebrew), I would say yes. The more familiar one is with realia, the better one can understand gemara and Tanach as it was intended.I would suspect, given the Yerushalmi, that the Babylonian Amoraim in our gemara were also familiar with the Paleo-Hebrew tav, such that the mark made on the forehead was either simply a mark, or an X. In which case they understood their own remarks to be midrash.
There is a discussion of how in the Ten Commandments, engraved through and through on two tablets, the samach and mem sofit were miraculous, in that the middle portion had to have floated (Shabbat 104a and Megilla 2b-3a). How to understand the Yerushalmi that has instead "ayin and tes?" You need to know Ktav Ivri (in which these two letters are circular - the ayin looks like a samach, and the tes looks like an X inside an O, in what seems a modification of the letter tav) - to really understand this - and it is clear that Chazal knew Ktav Ivri.
Also, to understand Yechezkel 9:4 and 9:6 about the "mark," the "tav" made on people's foreheads. Does this mean a random mark? Does this mean something that looks like the Ktav Ashuri ת? It makes a lot more sense when you know the Ktav Ivri Tav looks like an X.
You never know when arcane knowledge can be useful.
It is always useful to understand peshat in the pesukim alongside the midrashic explanation.