Salah of Allah on the Messenger is Allah’s praise and mention of him to the sublime assembly ( consisting of angels and pure souls). There is another view held by some scholars: It denotes Allah’s bestowal of mercy and high status on him.
However, Imam Ibn Hajar after citing the two opinions says: The preferred view is that of Abu al-Aliyah: "Allah’s Salah on the Prophet denotes His praising him and exalting his rank with Him. Angels Salah on the Prophet means their entreating Allah to bestow on him the above-exalted status."
Having said this, let me point out while trying to make sense of out of such issues, we must never get carried away by digging into matters of Ghayb - especially as related to the description of attributes or actions of Allah bsince such matters are beyond our ken of perception.
Therefore, we may do well to carry out the bidding of Allah: In this particular case, it involves sending salutations on the Prophet (peace be upon him) unceasingly so that we derive infinite blessings.