Seven hundred years before Christ (i.e., Messiah) was born, the prophet Isaiah was told that He would be one person with two natures—divine and human.
At a time of great crisis for Israel, the house of David was given a great promise. “Then he said, ‘Hear now, O house of David! Is it a small thing for you to weary men, but will you weary my God also? Therefore the Lord Himself will give you a sign: Behold, the virgin shall conceive and bear a Son [i.e., fully human], and shall call His name Immanuel [i.e., God with us, fully divine]’” (Isa. 7:13-14). In the very next chapter, the prophet is told that the God of Israel is “Immanuel” (Isa. 8:8; cf. 8:10).
But how could a virgin have a child? That was the urgent question that Mary asked Gabriel, the messenger-angel sent from God: “How can this be, since I do not know a man?” (Luke 1:34). The answer was astounding, and is recorded by Luke, “the beloved physician” (Col. 4:14): “And the angel answered and said to her, ‘The Holy Spirit [i.e., the third person of the triune God] will come upon you, and the power of the Highest will overshadow you; therefore, also, that Holy One who is to be born will be called the Son of God…. For with God nothing will be impossible’ ” (Luke 1:35-37).