Mosiah 8:16

And Ammon said that a seer is a revelator and a prophet also; and a gift which is greater can no man have, except he should possess the power of God, which no man can; yet a man may have great power given him from God.

God does not grant to men all of his power. Some powers are simply not meant for mortals. The power of resurrection, for example, is not given to man. The Lord holds that power for himself. Yet man can be granted power through the priesthood to raise the dead and call them forth from death to return to mortality. Those so raised,  however, are still mortal and will again have their spirits separated from their bodies, to await like all mortals the permanent reuniting of body and spirit that is the God-given gift of resurrection. We as mortals can receive great power over earthly things, but God reserves power over heavenly things.