Helaman 8:18

Yea, and behold I say unto you, that Abraham not only knew of these things, but there were many before the days of Abraham who were called by the order of God; yea, even after the order of his Son; and this that it should be shown unto the people, a great many thousand years before his coming, that even redemption should come unto them.

The existence of the restored priesthood is proof that salvation is achievable. Why would God grant men authority to perform saving ordinances if salvation were not obtainable? Why would he grant men power to heal illness and afflictions if we just die and rot in the grave? Why would he give us the temple if exaltation in the celestial kingdom is out of reach?  The very fact that we have the priesthood is a sign of hope from God.

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.

Second Nephi 1:25

And I exceedingly fear and tremble because of you, lest he shall suffer again; for behold, ye have accused him that he sought power and authority over you; but I know that he hath not sought for power nor authority over you, but he hath sought the glory of God, and your own eternal welfare.

The righteous exercise of priesthood authority is always to glorify God and serve others. The righteous seeking of power is to enable us to serve better.  When that is our motivation,  God is pleased with us and will grant us all the power we can safely use.