D&C 84

Knowing that God created man on the seventh day, suggest that the word "rest" in God's terminology is not the same as ours.  In fact, He says -

"...this is my work and my glory—to bring to pass the immortality and eternal life of man."  (Pearl of Great Price | Moses 1:39)

It sounds to me that this is his definition of rest. He also states that -

"...in the ordinances thereof, the power of godliness is manifest.
21 And without the ordinances thereof, and the authority of the priesthood, the power of godliness is not manifest unto men in the flesh;
22 For without this no man can see the face of God, even the Father, and live.
23 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..."  (Doctrine and Covenants | Section 84:20 - 23)

It appears to me that His rest is the work of sanctifying men.  Rest is also defined as the Lord continues -

"...which rest is the fulness of his glory."  (Doctrine and Covenants | Section 84:24)

His rest then is the fullness of His glory which is His "work and glory".