The Hebrew Immanuel (H6005) is a compound name: im (with) + anu (us) + El (God) = 'God with us.' It appears first in Isaiah 7:14: 'Therefore the Lord himself will give you a sign: The virgin will conceive and give birth to a son, and will call him Immanuel.' The name reappears in Isaiah 8:8 and 8:10 as a title of divine assurance: the land is 'your land, O Immanuel' (v.8) and the plot of the nations will fail 'for God is with us' (Immanuel) (v.10).
Immanuel is one of the most theologically loaded proper names in the OT. Its fulfillment in Matthew 1:23 is the hinge of all redemptive history: the eternal Son of God taking human flesh so that 'God with us' becomes not a promise but a physical reality. The entire arc of Scripture moves toward Immanuel: God walking with Adam in the garden, dwelling in the tabernacle and temple, incarnated in Jesus of Nazareth, indwelling the church by the Spirit (John 14:16-17), and finally dwelling with His people forever in the New Jerusalem (Revelation 21:3: 'God's dwelling place is now among the people, and he will dwell with them').