The following passage was directed at unbelieving folks in the Old Testament, but is just as applicable today.
41 Behold, ye
despisers, and wonder, and perish: for I work a work in your days, a work which
ye shall in no wise believe, though a man declare it unto you.
Jesus rehearsed a similar warning to those around Him before He was sacrificially crucified, once, for our all of our sin, for all time. He did that for you and me, and every person, so that we can know 100% for sure that we are saved from the consequences of our sin, if we will but choose to repent of our sin, and accept Him and His sacrifice on our behalf.