I will give thanks to the LORD with my whole heart; I will recount all of Your wonderful deeds.
Confess is a single word in Hebrew that among Hebrews means as much as all these among us: praise, give thanks, recompense, and acknowledge a benefit received. . .. Some people confess with their lips only. They are the ones who say one thing in the heart and another with the mouth, like the sinner who has evil intentions and sings to God nevertheless. Concerning them Psalm 78:36-37 says: "They lied to Him with their tongue, but their heart was not right before Him." Others confess with their heart, but not with the whole heart. These are the ones who confess with half a heart and do not do, or do sluggishly, what they say and understand. But those confess with the whole heart who are ready to do and suffer with all their powers, just as it is in their hearts.
From First Lectures on the Psalms, on Psalm 9 (Luther's Works 10:91-92)