Therefore this iniquity - That is, this refusing to trust in Yahweh, and this intention to seek the alliance of Egypt. The general sense of the figure here is, that their depending on Egypt would involve them ultimately in complete and awful ruin - ruin that should come upon them as suddenly as when a wall that had been long swelling out gives way.
As a breach ready to fall - Like a breaking forth, or a bursting in a wall.
Swelling out in a high wall - That is, where the foundation is not firm, and where one part of the wall sinks, and it inclines to one side until it suddenly bursts forth. A similar figure is used by the Psalmist Psalms 62:3 :
Ye shall be slain all of you
As a bowing wall shall ye be, and as a tottering fence.
Whose breaking cometh suddenly - Though it has been long leaning and swelling, yet the actual bursting forth would be in an instant. So would it be with the destruction that would come upon the Jews. Though by their sins they had been long preparing for it, yet it would come upon them by a sudden and tremendous crash. So it will be with all sinners. Destruction may seem to be long delayed - as a wall may be long inclining, and may seem to prepare imperceptibly to fall; but in due time it will come suddenly upon them, when too late to obtain relief.