isaiah 7:14 Therefore the Lord himself shall give you a sign; Behold, a virgin shall conceive, and bear a son, and shall call his name Immanuel. - Free Bible Online

      14. himself--since thou wilt not ask a sign, nay, rejectest the offer of one.
      you--for the sake of the house of believing "David" (God remembering His everlasting covenant with David), not for unbelieving Ahaz' sake.
      Behold--arresting attention to the extraordinary prophecy.
      virgin--from a root, "to lie hid," virgins being closely kept from men's gaze in their parents' custody in the East. The Hebrew, and the Septuagint here, and Greek (Mt 1:23), have the article, the virgin, some definite one known to the speaker and his hearers; primarily, the woman, then a virgin, about immediately to become the second wife, and bear a child, whose attainment of the age of discrimination (about three years) should be preceded by the deliverance of Judah from its two invaders; its fullest significancy is realized in "the woman" (Ge 3:15), whose seed should bruise the serpent's head and deliver captive man (Jer 31:22; Mic 5:3). Language is selected such as, while partially applicable to the immediate event, receives its fullest, most appropriate, and exhaustive accomplishment in Messianic events. The New Testament application of such prophecies is not a strained "accommodation"; rather the temporary fulfilment of an adaptation of the far-reaching prophecy to the present passing event, which foreshadows typically the great central end of prophecy, Jesus Christ (Re 19:10). Evidently the wording is such as to apply more fully to Jesus Christ than to the prophet's son; "virgin" applies, in its simplest sense, to the Virgin Mary, rather than to the prophetess who ceased to be a virgin when she "conceived"; "Immanuel," God with us (Joh 1:14; Re 21:3), cannot in a strict sense apply to Isaiah's son, but only to Him who is presently called expressly (Isa 9:6), "the Child, the Son, Wonderful (compare Isa 8:18), the mighty God." Local and temporary features (as in Isa 7:15, 16) are added in every type; otherwise it would be no type, but the thing itself. There are resemblances to the great Antitype sufficient to be recognized by those who seek them; dissimilarities enough to confound those who do not desire to discover them.
      call--that is, "she shall," or as Margin, "thou, O Virgin, shalt call;" mothers often named their children (Ge 4:1, 25; 19:37; 29:32). In Mt 1:23 the expression is strikingly changed into, "They shall call"; when the prophecy received its full accomplishment, no longer is the name Immanuel restricted to the prophetess' view of His character, as in its partial fulfilment in her son; all shall then call (that is, not literally), or regard Him as peculiarly and most fitly characterized by the descriptive name, "Immanuel" (1Ti 3:16; Col 2:9).
      name--not mere appellation, which neither Isaiah's son nor Jesus Christ bore literally; but what describes His manifested attributes; His character (so Isa 9:6). The name in its proper destination was not arbitrary, but characteristic of the individual; sin destroyed the faculty of perceiving the internal being; hence the severance now between the name and the character; in the case of Jesus Christ and many in Scripture, the Holy Ghost has supplied this want [OLSHAUSEN].

JFB.