Psalms 103:17
But the mercy of the LORD is from everlasting to everlasting upon them that fear him, and his righteousness unto children’s children; But the mercy of the LORD is from everlasting to everlasting upon them that fear him, and his righteousness unto children’s children;
The mercy of the Lord rests upon those who fear Him from everlasting to everlasting, lasting forever without end. His righteousness extends to their children and grandchildren, unto children's children and descendants after them. This enduring promise belongs to those who keep His covenant and remember His precepts and commandments in order to obey and do them, as the following verse or verses explain. Those who fear Him are thus identified as those who keep His covenant and remember His commandments to do them.
In contrast to human life, which is brief and passes like a shadow, God's word and covenant mercy and faithfulness stand permanently and endure forever. His mercy and righteousness so endure for those who fear Him and for their children. This endurance gives ground for confidence in God's everlasting, sure covenant. It assures enduring mercy in connection with David's repentance and forgiveness.
The extension of His righteousness to children's children shows the lasting influence parents may have on their children. Keeping His commandments brings great reward even in this life. That reward includes a conscience that does not condemn and a heart at peace with God rather than at enmity with Him. His mercy toward those who fear Him includes personal help in answer to prayer, so that relief received in a time of severe pain is recognized as an instance of that mercy.