Maybe for the same reason we have 'kiddy-garden' as well as grad school.
Spiritually not everyone is ready for the 'deeper truths' and some will never be.
Is there no place for someone who just gets saved and likes to sit in church, feel good and praise the Lord?
We all don't need to learn Latin, Greek or Estrangelo Aramaic in order to serve, do we?
>>Spiritually not everyone is ready for the 'deeper truths' and some will never be.<<
Direct contradiction to scripture. We are to constantly be growing in grace, sanctifying ourselves, and mortifying our sins - running with endurance the race that is set before us.
>>Is there no place for someone who just gets saved and likes to sit in church, feel good and praise the Lord?<<
Sounds pretty lazy and luke-warm to me. A regenerate heart has a deep, unquenchable yearning for deeper spiritual truths. I have yet to meet a saved person who was content to hang out in kindergarten and sing songs all day.
I can't imagine God using the Holy Spirit to convict a sinner, then leaving them on "idle". Unless you've got some heretofore unknown bit of scripture that says otherwise.