מלכים א, פרק א׳, פסוק ל׳

A long-held promise regarding the royal succession is suddenly brought into immediate action. King David had previously made a clear oath that Solomon would be the one to inherit the throne and rule in his place [מצודת ציון]. Originally, the expectation was that this transition of power would only take place after David passed away.

However, the king decides to change the timeline and act right away. Rather than waiting, David declares his intention to fulfill his oath on that very day. By choosing to crown Solomon immediately while he is still alive, he takes practical steps to guarantee that his promise is securely established and that Solomon will indeed be his successor [מצודת דוד, ביאור שטיינזלץ].