The Spirit Of Faith & the Spirit of Unbelief by Dr Michael H Yeager

SMITH WIGGLESWORTH:
The greatest sin in all the world is “unbelief.” It will cut off from you everything that God has for you. It will hinder your progress, and darken the prospects of your life. It will shut heaven off and open hell up; but if you believe God your faith will shut off hell and open heaven. Faith is the substance of things hoped for and the evidence of things not seen. Unbelief will cause you to put your trust in the arm of the flesh, instead of Trusting the God of Heaven who can not lie! Link to a book about unbelief:
Smith Wigglesworth: OVERCOMING THE SPIRIT OF UNBELIEF & DOUBT Kindle Edition
https://www.amazon.com/gp/product/B09BZZZ913/ref=dbs_a_def_rwt_hsch_vapi_taft_p1_i0