This is a reference to the refusal of the ancient Israelites, under Moses, to receive the further light and knowledge which the Lawgiver sought to give them, including the fulness of the blessings of the priesthood and thus the privilege of coming into the divine presence.
“And this greater priesthood administereth the gospel and holdeth the key of the mysteries of the kingdom, even the key of the knowledge of God. Therefore, in the ordinances thereof, the power of godliness is manifest.
“And without the ordinances thereof, and the authority of the priesthood, the power of godliness is not manifest unto men in the flesh; for without this”-the power of godliness-“no man can see the face of God, even the Father, and live.
“Now this Moses plainly taught to the children of Israel in the wilderness, and sought diligently to sanctify his people that they might behold the face of God; but they hardened their hearts and could not endure his presence; therefore, the Lord in his wrath, for his anger was kindled against them, swore that they should not enter into his rest while in the wilderness, which rest is the fulness of his glory.”
(D&C 84:19-24; see also JST, Exodus 34:1-2; JST, Deuteronomy 10:1-2; Psalms 95: 11; Hebrews 3:11.)