What three things are indispensable for a believer, according to Shaykh Abdul Qadir Gilani?

Shaykh Abdul Qadir Gilani rahimahullah names three things that a believer should not be without in all conditions of life, in the first discourse of Futuh ul-Ghaib, The Revelations of the Unseen.

That first discourse covers the concept of life for a Muslim in faith, belief and actions, encouraging him to engage with mind, body and soul, and this is the precise definition of a Sufi:

"Three things are indispensable for a believer in all conditions of life: First, he should keep the commandments of Allah. Second, he should abstain from the forbidden things and third, he should be pleased with the decree of Providence. Thus, the least that is expected of a believer is that he should not be without these three, so he should make up his mind for these and talk to himself about these and keep his organs engaged in them." [Gilani, The Revelations of the Unseen, Futuhul Ghaib]