The "messianic prophecies" cited by Christians are in the past tense. Therefore they cannot refer to a future, coming Messiah.
There is no such thing as "tense" in biblical Hebrew.(Modern Hebrew, on the other hand, does have tenses.) Biblical Hebrew is not a "tense" language. Modern grammarians recognize that it is an "aspectual" language. This means that the same form of a verb can be translated as either past, present, or future depending on the context and various grammatical cues. The most well known grammatical cue is the "vav-consecutive" that makes an imperfective verb to refer to the past.
Therefore it is wrong to say that Isaiah 53 or other prophecies are in the "past tense." BIblical Hebrew has no tenses. There are many examples of what is wrongly called the "past tense" form (properly called "the perfective" or "perfect") being used for future time.
This fact was recognized by the medieval commentators as well as by modern grammarians.
Medieval Jewish grammarian and commentator David Kimchi on the prophets' use of the perfect for future events:
"The matter is as clear as though it had already passed."
-- David Kimchi, Sefer Mikhlol. Cited in Waltke, Bruce K. and O'Connor, Michael Patrick. An Introduction to Biblical Hebrew Syntax (Winona Lake, IN: Eisenbrauns, 1990), p. 464 n. 45. They reference Leslie McCall, The Enigma of the Hebrew Verbal System: Solutions From Ewald to the Present (Sheffield: Almond, 1982), p. 8.
Rabbi Isaac ben Yedaiah (13th c.)
[The rabbis] of blessed memory followed, in these words of theirs, in the paths of the prophets who speak of something which will happen in the future in the language of the past. Since they saw in prophetic vision that which was to occur in the future, they spoke about it in the past tense and testified firmly that it had happened, to teach the certainty of his [God's] words -- may he be blessed -- and his positive promise that can never change and his beneficent message that will not be altered.
-- Saperstein, Marc. "The Works of R. Isaac b. Yedaiah." Ph.D. dissertation, Harvard University, 1977, pp. 481-82. Cited in Daggers of Faith by Robert Chazan, Berkeley: UC Press, 1989, p. 87.
From the standard grammar of Biblical Hebrew, Gesenius' Hebrew Grammar (section 106n, pp. 312-313):
More particularly the uses of the perfect may be distinguished as follows: -- ...To express facts which are undoubtedly imminent, and, therefore in the imagination of the speaker, already accomplished (perfectum confidentiae), e.g., Nu. 17:27, behold, we perish ,we are undone, we are all undone. Gn. 30:13, Is. 6:5 (I am undone), Pr. 4:2....This use of the perfect occurs most frequently in prophetic language (perfectum propheticum). The prophet so transports himself in imagination into the future that he describes the future event as if it had been already seen or heard by him, e.g. Is. 5:13 therefore my people are gone into captivity; 9:1ff.,10:28,11:9...; 19:7, Jb. 5:20, 2 Ch. 20:37. Not infrequently the imperfect interchanges with such perfects either in the parallel member or further on in the narrative.
David ("Fortress of David," 18th c. commentary by David Altschuler) on Jeremiah 31:32:
"I will place -- lit. I placed. This is the prophetic past. I will incline their hearts to keep the Torah."
-- Cited in Rosenberg, A. J. Jeremiah: A New English Translation. New York: The Judaica Press, 1985, vol. 2, p. 255.
Contemporary Jewish commentator Nahum Sarna on Exodus 12:17, "for on this very day I brought your ranks out of the land of Egypt":
This is an example of the "prophetic perfect." The future is described as having already occurred because God's will inherently and ineluctably possesses the power of realization so that the time factor is inconsequential.
-- Exodus: The Traditional Hebrew Text with the New JPS Translation (Philadelphia: Jewish Publication Society, 1991), p. 59.
From the recent textbook of Biblical Hebrew, An Introduction to Biblical Hebrew Syntax (Sec. 30.5.1.e, pp. 489-490):
Referring to absolute future time, a perfective form may be persistent or accidental. A persistent (future) perfective represents a single situation extending from the present into the future.
- Until when will you refuse to humble yourself before me? Exod 10:3
With an accidental perfective a speaker vividly and dramatically represents a future situation both as complete and as independent.
- And concerning Ishmael . . . I will bless him. Gen. 17:20.
- Women will call me happy. Gen. 30:13.
- We will die. We are lost, we are all lost. Num. 17:27.
This use is especially frequent in prophetic address (hence it is also called the "prophetic perfect" or "perfective of confidence").
- I see him, but not now; I behold him, but not near. A star will come out of Jacob. Num. 24:17.
- In the past he humbled . . . in the future he will honor . . . The people walking in darkness will see a great light. Isa. 8:23-9:1.
-- Waltke and O'Connor [full reference given above], pp. 489-490.