The Lord of hosts is with us. This is the ground of assurance. Our God, Jehovah, is "the Lord of hosts"—one who has countless angels at his command (2 Kings 6:16, 2 Kings 6:17; Psalms 68:17; Matthew 26:53).
And he is "with us"—on our side, ready to help. The God of Jacob is our Refuge; i.e. our covenant God, the God who entered into covenant with our fathers, Abraham, Isaac, and Jacob.