King David stands completely overwhelmed by the massive promises God has just made regarding the future of his royal line. Faced with such an extraordinary guarantee, words simply fail him. He is left with a profound sense of humility, recognizing that God understands his needs and his innermost thoughts far better than he could ever articulate.
The primary approach among commentators is that David simply cannot find anything else to ask for. God has already provided for him and promised to secure the future of his descendants, leaving him without a single remaining request [רש״י, מצודת דוד]. Beyond having all his needs met, David feels entirely unworthy of such an enormous promise [ביאור שטיינזלץ]. He realizes that as a mere mortal, he has absolutely nothing to add to God's supreme and infinite knowledge [מלבי״ם]. Taking a slightly different angle, another perspective suggests that David's silence does not stem only from a lack of requests, but from a genuine struggle to find the right words. His heart is so overflowing with deep gratitude that he simply does not know how to express it [רד״ק].
Unable to properly voice his feelings, David relies entirely on the fact that God knows him intimately. This divine knowledge carries several layers of meaning. On one level, it is an expression of deep love, mercy, and personal care [מצודת ציון]. Because God knows David so well, He mercifully provides for all his needs before David even has the chance to ask [רש״י, מצודת דוד]. On another level, this knowledge refers to a direct connection to the heart. Even when David is completely speechless, God reads his thoughts, understands exactly what he feels, and fully accepts his silent prayer [רד״ק].
A deeper layer of this knowledge relates to the dimension of time. God does not merely know David in the present moment; He has known him from the very beginning. God's knowledge is absolute and supreme [מלבי״ם], existing since ancient times. Because God's thoughts and words shape reality long before events actually unfold in the world, David's destiny as king was already secured, rooted in the ancient promises made to Abraham. Consequently, David realizes he has no need to offer extra words of affection to convince God to treat him well, for God had already known him and decreed goodness for him long ago [אלשיך].