Charles Ellicott Commentary Isaiah 25:4

"For thou hast been a stronghold to the poor, a stronghold to the needy in his distress, a refuge from the storm, a shade from the heat, when the blast of the terrible ones is as a storm against the wall." — Isaiah 25:4 (ASV)

You have been a strength ... —Literally, a fortress. The fierceness of the oppressor is represented by the intolerable heat, and the fierce tornado of an eastern storm, dashing against the wall, threatening it with destruction. From that storm the faithful servants of the Lord should find shelter as in the castle of the great King.