Like most christians working in the sciences I struggle to
sort out the relation between faith and reason. I think
that John's position is little extreme for me. I think that
there is a difference between rationalism and being
rational. i.e we are not argued into the kingdom (though
C.S. Lewis' account of his own conversion comes prretty
close), but rather this is the work of the Holy Spirit.
Nevertheless our faith is NOT irrational. Otherwise books
like Mere Christianity, Who Moved the Stone, and other such
stuff would be at best irrelevant. Others have argued that
our faith also is not strictly speaking rational, but
suprarational and that is perhaps what John is arguing.
I put this is the context of faith that is for the whole
person, body mind and spirit; that we serve God with all our
heart, mind, soul, and strength.