Indeed the safest road to Hell is the gradual one — the gentle slope, soft underfoot, without sudden turnings, without milestones, without signposts,… - C. S. Lewis

The Guide sang: Nearly they stood who fall; Themselves as they look back See always in the track The one false step, where all Even yet, by lightest swerve Of foot not yet enslaved, By smallest tremor of the smallest nerve, Might have been saved. Nearly they fell who stand, And with cold after fear Look back to mark how near They grazed the Siren's land, Wondering that subtle fate, By threads so spidery fine, The choice of ways so small, the event so great, Should thus entwine. Therefore oh, man, have fear Lest oldest fears be true, Lest thou too far pursue The road that seems so clear, And step, secure, a hair-breadth bourne, Which, being once crossed forever unawares, Denies return.

He begins to think for himself and meets Nineteenth-century Rationalism Which can explain away religion by any number of methods.

The Spirit of the Age wishes to allow argument and not to allow argument. … If anyone argues with them they say that he is rationalizing his own desires, and therefore need not be answered. But if anyone listens to them they will then argue themselves to show that their own doctrines are true. … You must ask them whether any reasoning is valid or not. If they say no, then their own doctrines, being reached by reasoning, fall to the ground. If they say yes, then they will have to examine your arguments and refute them on their merits: for if some reasoning is valid, for all they know, your bit of reasoning may be one of the valid bits.