Matthew 7:14:

Because strait is the gate, and narrow is the way, which leads to life, and few there be that find it.

See also:

Does Scripture Promise a Mighty Worldwide End-Time Revival?
Objection: Mark 16:18 Does Not Say, “They Shall Recover IF They Have Enough Faith,” Yet Faith Healers Blame the Sick for Not Believing
Objection: We Should Use Our Faith for Souls Rather Than Selfishly Seeking Our Own Healing