The context of this warning is the reluctance of some to provide for the physical welfare of their pastors and teachers, and Paul makes this a matter of self-deception. Why? Because those who hold back from proper support of their pastors are trying to cheat God.
What does God expect of us? Do we have to pay for a spiritual blessing with money? No, money cannot buy anything as precious as what we receive from God; there is no direct correlation, and yet if we are not willing to give this token remittance for what is worth far more than any monetary gift, we show that we do not understand the value of what we receive.