I think it's more "the government must spend to be able to tax"?

I'm no expert on this, but I think that wording suggests that the government's goal is to tax, but it seems to me that a government really wants to spend.

My understanding of MMT is that it removes the direct relationship between the ideas of spending and taxation, instead tying them both to inflation. Spending increases inflation by adding currency into circulation, and taxation decreases inflation by removing it from circulation. Although I'm not sure how that fits into a one-liner :)

Government also needs to tax to ensure sufficient demand for its money ("taxes drive money")