To express a purpose

The conjunction lest, indicating a negative purpose, generally introduces a subjunctive clause:
I eat lest I die.
I'll place the book back on the shelf, lest it get lost.

The conjunction in order that, indicating a positive purpose, also sometimes introduces a subjunctive clause, though it more commonly introduces a clause using the auxiliary verb may (or in the past tense, might):
I'm putting your dinner in the oven in order that it (may) keep warm.
He wrote it in his diary in order that he (might) remember