Saving grace (also called special grace) is the gift of salvation that includes supernatural regeneration of the heart and the indwelling of the Holy Spirit.
Before supernatural regeneration, people are "by nature the children of wrath, even as others. But God, who is rich in mercy, because of His great love with which He loved us, even when we were dead in trespasses, made us alive together with Christ (by grace you have been saved)" (Ephesians 2:3-5).

While common grace is given to all people, saving grace is given by God only to His elect:

"there is a remnant according to the election of grace. And if by grace, then is it no more of works: otherwise grace is no more grace. But if it be of works, then is it no more grace: otherwise work is no more work" (Romans 11:5-6).

Regeneration is supernatural, NOT NATURAL.

Saving grace IS NOT of the same nature as common grace. Since saving grace includes supernatural regeneration, it is of a different nature than common grace. The modern heresy that salvation is just a "tipping point" of the understanding came from the Scottish Common Sense Realism idea that saving grace is just a greater degree of common grace. John Witherspoon wrote of this belief in his
Treatise on Regeneration.

FALSE PREMISE 1: There is no difference between common and saving grace.
Witherspoon wrote: “There were … great debates whether special and common grace differ essentially in their nature, or if they differ only in degree… I embrace the last of these opinions”.

FALSE PREMISE 2: There is no difference between common and saving faith.
Witherspoon wrote: “What is faith? Is it any more than receiving the record which God hath given of his Son, believing the testimony of the Amen, the true and faithful Witness?”

Saving Faith is the Consequence of Saving Grace. For The New Light Calvinist, this also means Saving Repentance and Saving Faith are the result of regeneration and the indwelling of the Holy Spirit. "For by grace are ye saved through faith; and that not of yourselves: it is the gift of God". Saving grace is the cause of saving faith... anything other than consecutional faith is not saving faith.

For a complete explanation of the basis of the New Light Calvinist decision for Christ, please read Samuel Hopkins.