What is the difference between swearing by the Prophet (peace be upon him) and commanding something to be done through him?

There is no difference between the two phrases linguistically, as both are forbidden and prohibited in Sharia. Swearing by other than Allah is unlawful and impermissible; rather, it is a minor shirk, due to the Prophet's (peace be upon him) saying: "Whoever swears by other than Allah has disbelieved or committed shirk."