The 'hidden gateway' isn't an actual, physical door - so looking for it is 'in vain'. (This is a metaphor for how we search for happiness in the external world...and then wonder why it eludes us.)
The portal is the essence of Self beneath these shells of flesh - only the childlike innocence of faith can point the way and unlock it. (ie. true happiness and fulfillment can only be found within oneself.)
