grace is defined as courteous goodwill. Meaning, it's not asked for nor deserved, but is freely given. Mercy, on the other hand, is the compassion and kindness shown to someone whom it is in one's power to punish or harm. It is an act meant to relieve someone of their suffering

The Bible Dictionary puts it this way: “The main idea of the word [grace] is divine means of help or strength. … Grace is an enabling power