We are never in His favor because of our superior works. Psalm 136 thus summons us to give continual thanks to God for His mercy. Too often, when we pray, we forget to thank God for His mercy. We fall into the sin of expecting mercy and believing that we deserve it. This is why the reading of Psalm 136 is so wholesome.
Mercy is grace and good gifts to the undeserving.
Mercy is inseparable from grace because it means goodness to the undeserving, God s goodness out of sheer grace. The Bible speaks more often of God s grace and mercy than we do. We want God, as someone observed in the 1930s, as a spare tire, important to have in case of a flat tire, but nothing to think about otherwise.