Isa 1:4

1:4 Ah. This is an emphatic particle used in contexts of lament (1:4), but more often in threats (“woe,” 3:9, 11; 5:11, 18, 20, 21). The staccato lament decries the folly and evil of God’s children.

the Holy One of Israel. With his special designation for the Lord, Isaiah calls attention to the unique and awe-inspiring splendor of the Lord. The phrase occurs twenty-six times in Isaiah (e.g., 5:19, 24; 41:14, 16, 20; 60:9, 14). See also “the Holy One of Jacob” (29:23), “Holy One” (10:17; 40:25), and “your Holy One” (43:15).