Yahweh continues speaking to the people of Jerusalem in exile through Isaiah.
Yahweh speaks of blessing the people freely as if he were selling food and drink to needy people for free. (See: rc://en/ta/man/translate/figs-metaphor)
Come ... Come
The repetition of this word four times adds a sense of urgency to the invitation.
buy wine and milk without money and without cost
There is a sense of irony in this statement since a person usually has to use money to buy something. This emphasizes Yahweh's amazing grace in giving these things freely. (See: rc://en/ta/man/translate/figs-irony)