What is the meaning of the expression "birthpangs of Moshiach"?

The expression is used to denote the suffering that will come upon the Jewish people in the era immediately preceding the Redemption, which is similar to the pangs of labor that precede birth. This analogy is frequently found in the books of Prophets, such as "When she has not yet travailed, she has given birth; when the pang has not yet come to her, she has been delivered of a male child" (Isaiah 66:7) and "As a pregnant woman comes near to give birth, she shudders, she screams in her pangs, so were we because of You, O Lord" (Isaiah 27:16).

By extension, we can say that if the pain of Redemption is like labor, then exile is like pregnancy and Geulah is like birth. As described in Likutei Torah, a fetus in the womb lies “with its head between its knees, eats what its mother eats, its mouth is closed and its navel is open. When it emerges into the world's atmosphere, what was closed opens and what was open closes.” The fetus is complete with all its limbs, but they are not functional: “It has eyes that do not see, ears that do not hear.” Its mouth does not ingest food, and its nose does not breathe. They are dormant.

We are in a similar state in the time of exile. Indeed, we keep the Torah and its 613 mitzvot, which are compared to limbs of the body. Nevertheless, our spiritual senses are dormant, and only our lower faculties (the “navel”) are functional. Therefore we are incapable of sensing or apprehending G-dliness and spirituality.

When the Redemption comes we will finally emerge into the air – we will begin to use our spiritual senses. The "navel" – our channel to life in a materialistic, coarse environment – will close, and instead we will sustain ourselves through our higher organs in the head – our spiritual eyes, ears, nose and mouth. The Redemption is thus compared to a birth, when “what was open will close and what was closed will open.”

(Isaiah 66:7, 27:16. Torah Or Vaera, 55a. See also Ohr Hatorah, Shir Hashirim, section 2)