Learn how to teach a child critical thinking skills.
Do holidays! be the fun parent with birthday parties, Christmas, Easter, after school sports, band, arts, etc....
Visit various faiths to learn about world religions and to let your ex know in no uncertain terms that you will be teaching the child all about other faiths.
Teach the child it is more than ok to be an individual with their own thoughts, beliefs, likes and dislikes.
Teach the child to question everything even if it comes from you, dad, grandparents, teachers and especially religious authorities. When it is age appropriate teach them about cults.
Bring the child to a fun Sunday school! they do arts, crafts, dance, plays and so forth and still learn basic Bible stories. Quite a difference from a kh from what I hear.
Do all you can to protect your child's well being. Protect them from spiritual abuse, physical & sexual abuse, mental and emotional abuse. Be the mother bear and protect your child.