Charles H. Spurgeon on Psalms 110:3

In the beauties of holiness. This expression is usually read as if it belonged either to the words immediately preceding, or to those immediately following. But in either case the connection is somewhat difficult and obscure. It seems better regarded as a distinct and separate clause, adding a fresh trait to the description of the army. And what that is we need not find any difficulty in ascertaining. "The beauties of holiness" is a frequent phrase for the sacerdotal garments, the holy festal attire of the priests of the Lord. So considered, how beautifully it comes in here. The conquering King whom the psalm hymns is a Priest for ever; and he is followed by an army of priests. The soldiers are gathered in the day of the muster, with high courage and willing devotion, ready to fling away their lives; but they are clad not in mail, but in priestly robes; like those who wait before the altar rather than like those who plunge into the fight, like those who compassed Jericho with the ark for their standard and the trumpets tor all their weapons. We can scarcely fail to remember the words which echo these and interpret them. "The armies which were in heaven followed him on white horses, clothed in fine linen, white and clean" —a strange armour against sword cut and spear thrust. Alexander McLaren.