Malachi prophesied after the Temple had already been rebuilt, after its destruction by the Babylonians. By that time, the attitude of the Jews towards the Temple, and spiritual matters in general, had become apathetic. Furthermore, they had adopted many practices alien to the Spirit of the Torah.
Malachi portrays a debate between G-d and the People of Israel. The debate begins with G-d speaking first,
"I have loved you, says HaShem,
HaShem accuses the People of not showing Him proper honor, of bringing Him blind and lame sacrifices, of not even measuring up to the nations in fear of the L-rd! And the People have no response.
He accuses them of not being loyal to their wives,
Because the L-rd has been witness
HaShem declares that they have not observed the Laws of "Maaser," that require donation of one tenth of one's produce to the Levi, and proposes a test of His faithfulness and capability:
"Bring the whole tithe into the storehouse,
Malachi challenges the People to return to G-d "before the coming of the great and terrible day of the L-rd!"
"Behold, I will send you
"And he shall turn the heart of the fathers to the children,
After Malachi, the Talmud records that the gift of Prophecy was given to (holy) fools and madmen!
According to the RAMBAM, Malachi was a link in the Chain of "Mesorah," and received the Tradition of Torah from Baruch ben Neriah and his court.