My heart whispers good things. To inform you that they could not confess with their mouths until their hearts whispered in repentance and the Lord accepted them. Similarly, it says in Chronicles I 28:9, "And you, Solomon my son, know the God of your father, and serve Him with a perfect heart and with a willing mind, for the Lord searches all hearts and understands every plan and thought. If you seek Him, He will be found by you, but if you forsake Him, He will cast you off forever."
And all thoughts are only said in the heart, as it says in the same verse, "and every inclination of thoughts." Until a person restrains the thought in his holy heart, the Lord does not understand. Similarly, the sons of Korah were not able to sing with their mouths until their hearts whispered in repentance, and then they were immediately accepted. And why were they unable to sing?
Because Sheol was open beneath them, and fire was burning around them, as it says in Numbers 16:35, "And fire came forth from the Lord." In Psalm 106:17-18, it says, "The earth opened and swallowed up Dathan, and covered the company of Abiram. And a fire was kindled in their assembly." The sons of Korah saw that Sheol was open here and fire was there, and they could not confess with their mouths.
Therefore, my heart whispers. And why did it say "my heart whispers" if there were three of them and they were all equal in their hearts? It is to teach us that at one moment, one would have this thought in his heart, and at another moment, another would have the same thought in his heart, and all three were equal in one heart. Therefore, I say, "my actions are for the King."
If there is a whisper in my heart, why speak out loud? And if I speak out loud, why whisper? Rather, they said, "If we whispered in our hearts, we have already expressed our actions to the Lord." Therefore, I say, "my actions are for the King."
Another interpretation of "my heart whispers" is in prophecy, as they prophesied about the future. And similarly, Hannah said in Samuel I 2:6, "The Lord kills and brings to life."