But ye said, No; for we will flee upon horses; therefore shall ye flee: and, We will ride upon the swift; therefore shall they that pursue you be swift. But ye said, No; for we will flee - not as fugitives, but we will speed our course-namely, against the Assyrians, by the help of cavalry supplied by Egypt (Isaiah 31:1). This was expressly against the Mosaic law (Deuteronomy 17:16: cf. note, Isaiah 2:7; Hosea 14:3).
Therefore shall ye flee - literally, before your enemies. Their sin and its punishment correspond. Retribution in kind.