3 "Behold, a virgin shall conceive, and bear a son, and they shall call his name Immanuel, which being interpreted means, God with us." God with us means, Jesus, the Word of God, dwells in your heart so that you can hear and obey His teachings and commands: thus to have your heart and soul purified by His grace.
The following is how Christ in you, the hope of glory, Col 1:27, is fully formed in us to be with us:
We listen in humble silence and the words we hear him speak to us are Spirit and impart the life of God to us, John 6:63;
which life of God is Christ, John 1:5,14:6, so that Christ is formed within you, Gal 4:19.
Until finally Christ is fully formed and actually resurrected in you. 2 Cor 4:14, Col 2:11-12,3:1, Eph 2:5-6, Rom 8:11.
You then see Christ, the glory of God, appear in your heart and witness him bringing your salvation and eternal life.
This is the meaning of God with us, Immanuel. He really does wish to be with us: to dwell in us and walk in us: to be our true Lord guiding our thoughts with words to speak and works to His glory:
I will dwell in them, And walk in them. I will be their God, And they shall be My people. 2 Cor 6:16
That Christ may dwell in your hearts through faith..that you may be filled with all the fullness of God. Eph 3:17-19