Thy refuge, or, thy dwelling-place. Compare Psalms 91:1. Underneath, i.e. under thy arms to hold thee up, as my hands were once held up by Aaron and Hur. He will support and defend thee. Or the meaning is, Though he dwelleth on high, yet he comes down to the earth beneath to assist and deliver thee. Shall say, Destroy them, i.e. shall give thee not only command and commission, but also power, to destroy them; for God's saying is doing, his word comes with power.
Related Commentaries of Deuteronomy 33:27
Deuteronomy 33:27
27 The eternal God is thy refuge, and underneath are the everlasting arms: and he shall thrust out the enemy from before thee; and shall say, Destroy them.