Malbim: It already says "b'Derech Edvosecha Asati" (14) and "Edosecha Sha'ashu'ai" (24). They are testimonies that Hashem supervises over Tzadikim and pays their good reward. Therefore, it is very easy that they will tilt one's heart to serve Hashem for the sake of reward. He requests that Hashem lean his heart to the Edos themselves, to delight in them themselves, for they testify about His Hashgachah, goodness and Chesed, and not for reward and benefit.

Radak: My heart should not be avid to gather money, rather, it should be entirely to Your Edos. Batza is love of money - "Son'ei Vatza", for that verse already mentioned "Yir'ei Elokim Anshei Emes."