The Lord of hosts - The God commanding, ordering, marshalling the hosts of heaven - the angels, and the starry worlds. See the notes at Isaiah 1:9. Compare Psalms 24:10. The reference here is to God considered as having control over all “armies,” or all that can be regarded and described as a marshalled host, in earth and in heaven. Having such a Being, therefore, for a protector, they had nothing to fear. See Psalms 46:11.
Is with us - Is on our side; is our defender. The Hebrew phrase used here is employed in Isaiah 7:14 (notes); Isaiah 8:8 (notes), to describe the Messiah. See the notes at those passages.
The God of Jacob - See the notes at Psalms 24:6. The meaning is, The God whom Jacob acknowedged, and whom he found to be his friend, is with us.
Is our refuge - literally, a high place, as a tower, far above the reach of enemies. See Psalms 9:9, note; Psalms 18:2, note. So the margin, “an high place for us.”