Mercy is different from grace. Grace is the might of God at work in us to produce that which is humanly impossible. So a person actually living the “grace life” cannot fall short of the standard of scripture. Paul said, “when they saw the grace given to me…” He spoke of grace as the effectual working of the might of God in him that created a distinction which made the Church at Jerusalem accept his calling and they extended the right hand of fellowship to him. In other words, “no man can do what you are doing except God be with him.”
When a person falls short of the standard of God, then he goes to God for mercy, for the forgiveness of sins. He or she then goes back to a solid confession of their faith to receive grace in prayer to walk in obedience to God. There is a distinction between mercy and grace.