What is the meaning of "Al-Salat wa al-Salam" upon the Messenger of Allah, may Allah bless him and grant him peace?

Scholars have agreed that sending prayers upon the Prophet, peace and blessings be upon him, is mercy from Allah, supplication for forgiveness from the angels, and a prayer from humankind. Others, however, hold that it is Allah's praise of him in the Most Exalted Assembly. As for sending salutations upon him, peace and blessings be upon him, it is a prayer for the safety of his body and the preservation of his religion, and for his safety from the horrors of the Day of Resurrection. It may also include the safety of his Sunnah and Sharia from tampering. This salutation is a prayer and not a direct address to him. It is uttered with the intention of conjuring his image as if he were present before us.