Exodus 5:9

“Let there more work be laid upon the men, etc.] Instead of lessening it, let it be increased, or “be heavy” f159 upon them, that it may oppress and afflict them and keep them down, and weaken their strength and their spirits, and diminish them: that they may labour therein; and have no leisure time to spend in idleness and sloth: and let them not regard vain words; or “words of falsehood” f160 and lies, such as were spoken by Moses and Aaron, promising them liberty and deliverance from their bondage, which he was determined never to grant, and so eventually make such words to appear to be vain and empty, falsehood and lies.”

“Vain words - Those of Moses and Aaron. Exodus 5:14”

“Let there more work be laid upon the men: Heb. Let the work be heavy upon the men vain words: Kg2 18:20; Job 16:3; Jer 43:2; Zac 1:6; Mal 3:14; Eph 5:6 Exodus 5:10”

“"Let the work be heavy (press heavily) upon the people, and they shall make with it (i.e., stick to their work), and not look at lying words." By "lying words" the king meant the words of Moses, that the God of Israel had appeared to him, and demanded a sacrificial festival from His people. In Exo 5:11 special emphasis is laid upon אתּם "ye:" "Go, ye yourselves, fetch your straw," not others for you as heretofore; "for nothing is taken (diminished) from your work." The word כּי for has been correctly explained by Kimchi as supposing a parenthetical thought, et quidem alacriter vobis eundum est. Exodus 5:12”