When the angel Gabriel appeared to Mary to tell her that she had been chosen to give birth to Jesus, he told her that she should not be afraid. Why? Because she would conceive this child through the power of the Holy Spirit and that child would be the Son of God. God would be with Mary in the form of this child to whom she would give birth.
When the angel of the Lord appeared to Joseph in a dream to tell him that he should take Mary to be his wife, despite the fact that she was with child, he told Joseph not to be afraid. Why? Because the child that she was carrying was the Son of God, sent to save people from sin. The child would be called Immanuel, “God with us.” God would be with Joseph in the Son that he would serve as father to.
When the angel appeared to the shepherds to announce the birth of Jesus in Bethlehem, he told the shepherds not to be afraid. Why? Because he was bringing to them the good news that Jesus, the Savior, had been born. This child was the Son of God. God would be with the shepherds in the baby that they would find laying in a manger.
God gave us this promise through the prophet Isaiah: “Fear not, for I am with you; be not dismayed, for I am your God; I will strengthen you, I will help you, I will uphold you with my righteous right hand.” (Isaiah 41:10, ESV)
In the form of the child born in Bethlehem, Jesus, the Son of God was with us. When He ascended to heaven, He sent the Holy Spirit to be with us. When God is with us, we have no reason to fear, no cause to be afraid. Jesus told us that He will be with us until the end of the age (Matthew 28:20). We can stand on the promise that God is with us always, to give us strength when we are weak, to help us in our times of need, and to hold us up through times of trouble.