The so-called believers who deny the power of God flowing through the believer don't realize the danger they're in with their hard-hearted denial, because Jesus used the evidence of miracles to make the point that the Father lives in him. If you have Jesus living in you, you have the Father living in you as well. The miracles are not just evidence that believers will do these works, but also that the Father lives in the believer.
We see this truth in John 10:37-38 and in John 14:11
Do not believe me unless I do the works of my Father. But if I do them, even though you do not believe me, believe the works, that you may know and understand that the Father is in me, and I in the Father.” - John 10:37-38
Believe me when I say that I am in the Father and the Father is in me; or at least believe on the evidence of the works themselves. - John 14:11