Why have we been commanded to invoke blessings upon the Prophet and to ask Allah for the Wasilah and intercession for him, even though Allah Himself invokes blessings upon him and has already promised him both?

Prayers upon the Prophet, peace and blessings be upon him, are an obligation and a duty upon every Muslim. Allah’s prayers upon His Prophet signify His praise and exaltation of him. As for the prayers of angels and humans upon him, they are a request for Allah to bestow further blessings upon him. All of this is to illustrate his virtue and elevated status. Regarding the request for al-Wasilah for him, peace and blessings be upon him, despite its promised occurrence by Allah's word, the wisdom behind it lies in demonstrating his honor and great stature, and in the Muslims earning immense reward for supplicating for him.