According to LDS theology, one is saved by faith + works.  This is their gospel.

                For we labor diligently to write, to persuade our children, and also our 
                brethren, to believe in Christ, and to be reconciled to God; for we 
                know that it is by grace that we are saved, after all we can do. 
                2 Nephi 25:23 (Book of Mormon) 

The gospel according to the Bible is the good news that faith in the all-sufficing sacrificial death, burial, and resurrection of Jesus Christ gives 
you eternal life at the moment you believe.

For Christians, the desire to thank, praise, glorify, and honor God is the motivation behind good works. We cannot glorify God by seeking our own 
glory (that is; by performing works motivated by a desire to earn our own righteousness or eternal life). We are not saved by our works; but we are 
saved to do works. We reject Christ when we rely on our own works.

Obedience and works can never pay Jesus back: Galatians 2:16,21, Romans 4:14 (KJV). To attempt to do so is to stumble on the "Stumbling 
Stone of Zion" Romans 9:30-33.  It is an irony of Mormonism that the LDS church calls nonmembers Gentiles. We see this irony in the inspired words of Paul who identifies the stumbling stone of eternal life to those who try to obtain this eternal life through works.

          What then shall we say? That the Gentiles, who did not pursue righteousness, 
          have obtained it, a righteousness that is by faith; 31 but Israel, who 
          pursued a law of righteousness, has not attained it. 32 Why not? Because 
          they pursued it not by faith but as if it were by works. They stumbled 
          over the "stumbling stone." 33 As it is written: "See, I lay in Zion a 
          stone that causes men to stumble and a rock that makes them fall,
          and the one who trusts in him will never be put to shame."

On Judgment Day such people will stand in front of God and point to their own works. God will not respond favorably - Matthew 7:22-23. Such people stand condemned already and have fallen from grace. It is by faith that we are given righteousness from God (Galatians 5:4-5), not by works, lest one might boast Ephesians 2:8-9.

Romans 3:20-28:

Verse 20 - No one will be justified by deeds of the law, that is; by obedience.
Verse 20 - The purpose of the law is knowledge of sin, that is; to come to the knowledge that you are a sinner.
verse 21 - The law and the prophets (the old testament) witness that God's righteousness without the law is made known, that is; God's righteousness is separate from the law.

Verse 22 - God's righteousness comes through faith.

Verse 22 - Everyone who believes is given God's righteousness, it is not given based on being 'worthy' enough. See Genesis 15:6. It was Abram's faith which was credited to him as righteousness, that is; God considered Abram (who was a sinful man) righteous - even before his great works of faith.

In Romans 4:3 and/or Galatians 3:6, Paul repeats Genesis 15:6. We too are credited with righteousness because of our faith - not our worthiness.

From Romans 4:20-25 we see that we too become righteous through faith in God's promise that Jesus was delivered over to death for our sins and was raised to life for our justification.

Verse 23 - Everyone, because of their sin, is not righteous (fall short of God's glory) on their own.

Verse 24 - But we are freely justified (considered righteous, that is; perfect) by grace (grace = undeserved gift) because Jesus paid our penalty. There is no mention of us paying Jesus back, either partially or completely. 

Verse 25 - God allowed Jesus to propitiate his demand for payment. Through faith in Jesus' sacrifice (blood) we are given the credit.

verse 27 - There is no boasting in our righteousness because it does not come from works, but from faith, faith in what Jesus did.

Verse 28 - We are justified (made righteous, made pure, made perfect) through our faith, not by observing the law.

For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: 9 Not of works, lest any man should boast. Ephesians 2:8-9 (KJV)

No one will be declared righteous in his sight by observing the law. Romans 3:20