Psa 25:10 All the paths of the LORD are mercy and truth unto such as keep his covenant and his testimonies.
Here is the contrast of "Mercy" and "Truth".
In Psalms 25, we learn that God's merciful nature does not excuse us from sins. Some have the most perversed thought as to believe that by just WILLING to say sorry, he or she should be forgiven-because God promised so...or why wouldn't Jesus Christ's salvation be accomplished right after the fall of Adam if this salvation is the plan all along, as if the perplexity since the dawn of men's fall is undeserving. Such questions do not disturb me, but what does is when these are asked by Christian leaders directly or indirectly, not to give answer but instead to show how lacking they are in seeking God's Truth.
Many Christians have forgotten that mercy and truth work hand in hand. One cannot obtain mercy if one is not truthful, and neither can one be merciful if one is not truthful.
We pray for God's mercy, we beg for God's mercy. Some would twist the verses of Psalms 25 with their untruthfulness so that they can believe they DESERVE God's mercy and therefore viewing David's request as a hidden demand instead of a cried out hope.