Jamieson, Fausset and Brown on Isaiah 28:15

15. said--virtually, in your conduct, if not in words.

covenant--There may be a tacit reference to their confidence in their "covenant" with the Assyrians in the early part of Hezekiah's prosperous reign, before he ceased to pay tribute to them, as if it ensured Judah from evil, whatever might befall the neighboring Ephraim (Is 28:1). The full meaning is shown by the language ("covenant with death--hell," or sheol) to apply to all lulled in false security spiritually (Psa 12:4; Ec 8:8; Jr 8:11); the godly alone are in covenant with death (Job 5:23; Ho 2:18; 1Co 3:22).

overflowing scourge--two metaphors: the hostile Assyrian armies like an overwhelming flood.

pass through--namely, through Judea on their way to Egypt, to punish it as the protector of Samaria (2Ki 17:4).

lies--They did not use these words, but Isaiah designates their sentiments by their true name (Am 2:4).