The Hebrew word for mercy in this passage means: goodness, kindness, faithfulness.
The Hebrew word for truth means: firmness, faithfulness, sureness, reliability, stability, continuance; truth as spoken; truth of testimony and judgment, of divine instruction, as a body of ethical or religious knowledge.
If we stray from mercy and/or truth, we stray from the path of the Lord.
When we discover we have strayed from His path, the compass which leads us back to His path is found in the very heart of God (revealed in His Word) as we bow before His throne:
May we run to His throne of grace to obtain mercy and find grace to help in time of need.