Exodus 8:29

29 Moses said, “I am going to go out
The deictic particle with the participle usually indicates the futur instans nuance: “I am about to…,” or “I am going to….” The clause could also be subordinated as a temporal clause.
from you and pray to the Lord, and the swarms of flies will go away from Pharaoh, from his servants, and from his people tomorrow. Only do not let Pharaoh deal falsely again
The verb תָּלַל (talal) means “to mock, deceive, trifle with.” The construction in this verse forms a verbal hendiadys. The Hiphil jussive אַל־יֹסֵף (’al-yosef, “let not [Pharaoh] add”) is joined with the Hiphil infinitive הָתֵל (hatel, “to deceive”). It means: “Let not Pharaoh deceive again.” Changing to the third person in this warning to Pharaoh is more decisive, more powerful.
by not releasing
The Piel infinitive construct after lamed (ל) and the negative functions epexegetically, explaining how Pharaoh would deal falsely – “by not releasing.”
the people to sacrifice to the Lord.”
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