The chapter ends with a single, decisive statement. Whatever is offered in fire, whatever is given in charity, whatever austerity is practiced, whatever deed is done — if it is done without faith, it is called "asat." It bears no fruit in this world. It bears no fruit after death.
This is the thread that holds the entire chapter together. Krishna classified faith, food, sacrifice, austerity, and charity into three types. He taught the meaning of Om Tat Sat. And now he closes with the one principle that underlies all of it: without shraddha, nothing counts.
Faith is the foundation on which all of spiritual life stands. A building without a foundation cannot stand, no matter how grand it looks. In the same way, rituals, charity, and discipline without faith are hollow. That is the final word of Chapter 17.