Jamieson, Fausset and Brown on Isaiah 25:7

7. face of ... covering--image from mourning, in which it was usual to cover the face with a veil (2Sa 15:30). "Face of covering," that is, the covering itself; as in Job 41:13, "the face of his garment," the garment itself. The covering or veil is the mist of ignorance as to a future state, and the way to eternal life, which enveloped the nations (Ep 4:18) and the unbelieving Jew (2Co 3:15). The Jew, however, is first to be converted before the conversion of "all nations"; for it is "in this mountain," namely, Zion, that the latter are to have the veil taken off (Psa 102:13, 15, 16, 21, 22; Ro 11:12).