When practicing Qigong you want to empty your mind, to the degree that you want to calm down the voice in your head. That is, you want to reduce interference from your conscious mind.
Master Lin calls this becoming "one with the universe," or "one with God."
If what your Pastor says is true, then he is saying that your conscious mind is responsible for keeping "spirits" out. Since your conscious mind represents such a small portion of your brains capabilities, I sincerely doubt that it has that much power.
I understand that the belief that the conscious mind wards off spirits goes way back to before anyone had any understanding of the workings of the human brain. It is often easiest to cloak the unexplained in mysterious terms: "calm your mind and spirits will enter."
This is also a problem with the practice of Qigong, which goes back 5,000 years. Before it was understood, it, too, was mysteriously cloaked. One of the beauties of Spring Forest Qigong is that Master Lin presents it in simple terms that are based in how we now the body and mind operate.