From the additional notes to Charles Spurgeon's The Treasury of David, Psalm 119.
Verse. 65. Thou hast dealt well with thy servant, O Lord, according unto thy word
He knew that God's gifts are without repentance, and that he is not weary of well doing, but will finish the thing he hath begun; and therefore he pleads past favours. Nothing is more forcible to obtain mercy than to lay God's former mercies before him. Here are two grounds, First. If he dealt well with him when he was not regenerate, how much more will he now? and Secondly, all the gifts of God shall be perfectly finished, therefore he will go on to deal well with his servant. Here is a difference between faith and an accusing conscience: the accusing conscience is afraid to ask more, because it hath abused the former mercies: but faith, assuring us that all God's benefits are tokens of his love bestowed on us according to his word, is bold to ask for more. — Richard Greenham