Deuteronomy 31:18

“I will surely hide my face in that day, etc.] Which is repeated for the certainty of it, and that it might be taken notice of; that he was the spring and source of all their good things, their sun and their shield, who being withdrawn from them, they would be deprived of every thing that was good, and be liable to all evil; and this he would do, for all the evils which they shall have wrought; for all the immoralities they should be guilty of, every transgression of his law, whether of the first or second table, and especially idolatry: in that they are turned unto other gods; to the worship and service of them, which of all evils would be the most provoking to God; and the way of speaking…”

“The transaction recorded in these verses may be regarded as the solemn inauguration of Joshua to the office to which he had some time before Numbers 27:22 been called, and his recognition in it by God, which were manifested by his being summoned into the tabernacle with Moses while the Lord appeared in the pillar of cloud (compare Numbers 11:25; Numbers 12:5). Deuteronomy 31:16 The future apostasy of the people is announced in the presence of Joshua that the latter might be fully aware of the danger and strive in his day to avert it. This he faithfully did (compare Joshua 24:31); but we find him in his own last address to Israel repeating Joshua 23:15-16 the self-same prediction and warning.…”

“31:18 I will hide my face: The invisible God used this figure of speech (see study note on 8:2) to communicate the breaking of fellowship between himself and his people. He turned away to indicate his rejection and repudiation.”

“Deu 31:16, Deu 31:17 Deuteronomy 31:19”