Isaiah 21:5

Prepare — Furnish it with meats and drinks. The prophet foretells what the Babylonians would be doing when their enemies were at their doors. Watch — To give us notice of any approaching danger, that in the meantime we may more securely indulge ourselves. Princes — Of Babylon: arise from the table and run to your arms. Shield — Prepare yourselves and your arms for the approaching battle. The shield is put for all their weapons of offence and defence. They used to anoint their shields with oil, to preserve and polish them, and to make them slippery.