Exodus 13:5

5 When
Heb “and it will be when.”
the Lord brings you to the land of the Canaanites, Hittites, Amorites, Hivites, and Jebusites, which he swore to your fathers to give you, a land flowing with milk and honey,
See notes on Exod 3:8.
then you will keep
The verb is וְעָבַדְתָּ (veavadta), the Qal perfect with a vav (ו) consecutive. It is the equivalent of the imperfect tense of instruction or injunction; it forms the main point after the temporal clause – “when Yahweh brings you out…then you will serve.”
this ceremony
The object is a cognate accusative for emphasis on the meaning of the service – “you will serve this service.” W. C. Kaiser notes how this noun was translated “slavery” and “work” in the book, but “service” or “ceremony” for Yahweh. Israel was saved from slavery to Egypt into service for God as remembered by this ceremony (“Exodus,” EBC 2:383).
in this month.
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