In terms of context, Malachi was a post-exilic prophet, probably writing around 432-424 B.C. This makes him a contemporary with Ezra and Nehemiah. The temple had been rebuilt, but the expected restored golden age - a hope kindled by the prophecies of Zechariah and Haggai - had not arrived. Malachi thus predicted the coming of a great prophet, a new Elijah (3:23 NABRE, Malachi 4:5 KJV), who would fulfill the frustrated hopes of the people.
(Capitalization is an issue here, as the KJV capitalizes "He" thus making the messenger divine. Other translations - both Jewish and Christian - rightly leave word uncapitalized, for the messenger is later identified as Elijah, not the messiah.)
The OP asks about the offering and the tithe. This is found a little later in the same chapter. About the offerings:
3 He will sit refining and purifying silver,
and he will purify the Levites, Refining them like gold or silver,
that they may bring offerings to the Lord in righteousness. 4 Then the offering of Judah and Jerusalem
will please the Lord,
as in ancient days, as in years gone by.
Thus, the messenger or lord of the temple will restore the corruption of the Levites and thus make the offering of the people acceptable to God. Malachi indicates that although the temple had been restored, the priesthood had been corrupted. He does not specify but see Ezra 9:1. This prophecy may have been one of the reasons why, in the time of Jesus, the Qumran community (Essenes) placed great importance on the coming of a priestly messiah, even more than the royal one.
Regarding tithes:
8 Can anyone rob God? But you are robbing me! And you say, “How
have we robbed you?”
Of tithes and contributions! 9 You are indeed accursed,
for you, the whole nation, rob me. 10 Bring the whole tithe
into the storehouse, That there may be food in my house. Put me to the test, says the Lord of hosts, And see if I do not open the
floodgates of heaven for you,
and pour down upon you blessing without measure! 11 I will rebuke the locust for you
so that it will not destroy your crops, And the vine in the field will not be barren,
says the Lord of hosts.
Apparently, many people - having recently return from exile - were not fulfilling their duty to tithe, which in those days involved produce, more than money. Malachi called the nation to fill the storehouses of the temple with food and promised that those who offered their produce would be richly blessed with fertile crops and protected from locusts, etc.