Salvation is by grace, through faith, on the ground of Christ's finished work.
Three prepositions, three different jobs, and confusing them is where most errors start.
**By grace** — the cause. Grace means God's unearned favor toward people who have earned the opposite. Nothing in you started this. Paul says God commended his love toward us in that while we were yet sinners, Christ died for us. Not once we improved. While.
**Through faith** — the channel, not the cause. Faith is not a work you perform to qualify; it is the empty hand that receives. Faith does not save because it is strong or sincere. It saves because of who it is attached to. Weak faith in Christ saves; strong faith in yourself does not.
**On the ground of Christ's finished work** — the basis. On the cross Jesus said *tetelestai*, "It is finished" — a word used on ancient receipts to mean paid in full. Nothing was left owing. Salvation is not Christ's work plus yours; it is his work, received.
"Not of works, lest any man should boast" closes the door. If any part of salvation were earned, heaven would have a class system in it. It does not.
“For it is by grace you have been saved through faith, and this not from yourselves; it is the gift of God,”
By grace are ye saved through faith... it is the gift of God→
“But God proves His love for us in this: While we were still sinners, Christ died for us.”
While we were yet sinners, Christ died for us→
“When Jesus had received the sour wine, He said, “It is finished.” And bowing His head, He yielded up His spirit.”
It is finished→
“He saved us, not by the righteous deeds we had done, but according to His mercy, through the washing of new birth and renewal by the Holy Spirit.”
Not by works of righteousness which we have done→