This name is given to our Lord from his nature, as "God manifest in the flesh." For this reason, He is called Emmanuel, "God with us."
Let us take care that we have clear views of our Lord Jesus Christ's nature and person. It is a point of the deepest importance. We should settle it firmly in our minds that our Savior is perfect man as well as perfect God, and perfect God as well as perfect man. If we once lose sight of this great foundational truth, we may run into heresy. The name Emmanuel takes in the whole mystery. Jesus is "God with us." He had a nature like our own in all things, except without sin. But though Jesus was "with us" in human flesh and blood, He was at the same time completely God.
We shall often find, as we read the gospels, that our Savior could be tired and hungry and thirsty - could weep and groan and feel pain like one of us. In all this we see "the man" Christ Jesus. We see the nature He took on Him when He was born of the Virgin Mary.
But we shall also find in the same gospels that our Savior knew men's hearts and thoughts, that He had power over demons, that He could work the mightiest of miracles with a word, that He was ministered to by angels, that He allowed a disciple to call Him "my God," and that he said, "Before Abraham was I am," and, "I and my Father are one." In all this we see "the eternal God." We see Him "who is over all, God, blessed forever. Amen" (Romans 9:5).
Adapted from The Gospel of Matthew by J.C. Ryle (Chapter 1).