Generally, grace is the free, unmerited favor of God. Specifically, grace is the unmerited eternal salvation of God, which comes freely to the believing sinner as a gift through the atonement of Jesus Christ. It is receiving the opposite of what we deserve. It is the free forgiveness of sin and the offer of free imputed righteousness, which was purchased by Jesus Christ. This is the Gospel of the grace of Christ.
Salvation is entirely of grace.
This means it is exclusively a divine work, absolutely sovereign and free, in which sinners play no part and make no contribution. I must remind you that God is not obliged to save anyone. No one merits or deserves salvation. Grace, and grace alone, is the cause of salvation. But, the scheme of salvation taught by the Church of Rome is totally contrary to the Bible teaching that salvation is by grace alone.