Question: Is it impossible to receive salvation because no one can keep the commandments continually?

God does not remember our sins after we repent, and therefore to insist that Doctrine and Covenants 25:15 shuts everyone who has ever sinned out of God's presence is to deny the power of Christ to completely redeem us from our sins

Proponents of the argument that the LDS scriptures teach an "Impossible Gospel" point to Doctrine and Covenants 25:15-16 as an example of a requirement for salvation that cannot be fulfilled by humans.

God does not remember our sins after we repent, and therefore to insist that Doctrine and Covenants 25:15 shuts everyone who has ever sinned out of God's presence is to deny the power of Christ to completely redeem us from our sins. Mormons do not do so, and critics are either woefully ignorant of our and teaching or extremely deceptive if they suggest that we do.

These verses read:

"15 Keep my commandments continually, and a crown of righteousness thou shalt receive. And except thou do this, where I am you cannot come.
"16 And verily, verily, I say unto you, that this is my voice unto all. Amen."

[Verse 16 is relevant because it extends the prescription in verse 15 beyond Emma Smith, to whom the revelation is addressed, to everyone.]

Critics contend that because no one can keep the commandments continually, no one can return to God according to these verses. This is a misunderstanding, not only of Mormon doctrine and soteriology, but even of related Biblical teaching.

Short Answer

The Lord asks us to "keep my commandments continually", and repentance itself is a commandment. Dozens and dozens of passages can be used to show this, but one will do:

D&C 133:16 Hearken and hear, O ye inhabitants of the earth. Listen, ye elders of my church together, and hear the voice of the Lord; for he calleth upon all men, and he commandeth all men everywhere to repent.

Keeping the commandments continually includes continual repentance. The incredible blessing of repentance is made possible by the atonement of Christ, and it makes salvation possible for man.

Longer Answer: The Broader Context of LDS Soteriology

Consider 1 Timothy 6:11-12, where Paul commanded Timothy (and apparently all followers of God) the following:

"11 But thou, O man of God, flee these things; and follow after righteousness, godliness, faith, love, patience, meekness.
"12 Fight the good fight of faith, lay hold on eternal life, whereunto thou art also called, and hast professed a good profession before many witnesses."

Certainly a difficult and comprehensive command. But Paul didn't stop there, adding in verses 13 and 14:

"13 I give thee charge in the sight of God, who quickeneth all things, and before Christ Jesus...
"14 That thou keep this commandment without spot, unrebukeable, until the appearing of our Lord Jesus Christ."

There's no indication in that passage that failure in keeping that charge is acceptable. If there isn't a consequence for breaking it, it is nonsensical to call it a commandment.

More importantly, critics of Mormon soteriology ignore that one of the most-emphasized and oft-repeated commandments by the Lord, both in the Bible and in LDS scripture, is the commandment to repent.

Luke 13:3--"except ye repent, ye shall all likewise perish."
Mark 6:12--"And they went out, and preached that men should repent."
Matthew 3:2--"Repent ye, for the kingdom of heaven is at hand."
Alma 42:4--"And thus we see, that there was a time granted unto man to repent, yea, a probationary time, a time to repent and serve God."
Mosiah 26:30--"Yea, and as often as my people repent will I forgive them their trespasses against me."

Repentance, in LDS doctrine, is an act of forsaking past sin, being cleansed from its effects by the power of the Holy Ghost, and being fully reconciled again with God. Repentance completely restores an individual's worthiness and relationship with God--in Doctrine and Covenants 58:42 the Lord explains that "he who has repented of his sins, the same is forgiven, and I, the Lord, remember them no more." This means that, from the Lord's perspective, as long as we are continually repenting and continually striving to keep God's commandments, we will inherit a crown of righteousness.

A specific example is the instance in which Joseph Smith sinned by showing the ongoing Book of Mormon translation project to others against the Lord's command. Joseph was thoroughly chastised by the Lord and felt very distressed at his sin. But the Lord was clear that his failure to keep the commandments was not an absolute disqualification from God's favor: "Remember, God is merciful; therefore, repent of that which thou hast done which is contrary to the commandment which I gave you, and thou art still chosen, and art again called to the work." (Doctrine and Covenants 3:10.)

LDS doctrine fully accounts for man's fallen nature in its plan for providing a way back into the presence of God; it is disingenuous of critics to pretend that it does not. The Book of Mormon teaches extensively about the fall of Adam and humankind's consequent estrangement from God's perfection and presence. Mosiah 3:19 teaches that man's nature is an enemy to God and that a pervasive change is necessary. That change, as taught in Doctrine and Covenants 20:31, will fully sanctify a repentant man or woman:

"And we know also, that sanctification through the grace of our Lord and Savior Jesus Christ is just and true, to all those who love and serve God with all their mights, minds, and strength."

To sanctify means to make holy and pure, to in fact become the sort of person who can keep all commandments continually and who is "even as [Jesus Christ] [is]." (3 Nephi 28:10.) And this is done through Christ's grace, which is His power to change and save us when we choose to accept it by repenting.

Doctrine and Covenants 18:12 sums it up:

"And [Christ] hath risen again from the dead, that he might bring all men unto him, on conditions of repentance."

Therefore, taking into account the entirety of LDS doctrine, the verse in Doctrine and Covenants 25:15 commands keeping the commandments continually, which includes the commandment to repent. Humans will of course fail to keep each commandment perfectly, but can constantly desire to improve and strengthen their relationship with God. This is the spirit of repentance, which will bring the gift of Christ's grace and the power to overcome the desire to sin.

Notes

Question: Is it impossible to receive salvation because no one can keep the commandments continually?