OK, my little system is AT LEAST, EVEN IF. I provide definitions for religious concepts in the form of axioms in a manner that is compatible with naturalism (falsifiable and provable). Even in the sciences, we must admit we don’t have a complete understanding of most concepts, so AT LEAST could be applied to natural concepts too (the Universe, gravity, etc.)
Basically, this is a ground floor which doubt can dip no further. It allows us to always feel intellectually honest about pursuing God, religious ritual, fellowship and even Jesus himself.
God is AT LEAST the natural forces that created and sustain the Universe as experienced via a psychosocial construct rooted in evolved neurologic features in humans. EVEN IF that is a comprehensive definition for God, the pursuit of this personal, subjective experience can provide meaning, peace and empathy for others and is warranted.
Prayer is AT LEAST a form of mediation that encourages the development of healthy brain tissue, lowers stress and can connect us to God. EVEN IF that is a comprehensive definition of prayer, the health and psychological benefits of prayer justify the discipline.
The Bible is AT LEAST a set of writings where a people group describes their experience with and understanding of God over thousands of years. EVN IF that is a comprehensive definition of God, study of scripture is warranted to understand our culture and the way in which people come to know God.
Jesus is AT LEAST the idea of a man so connected to God that he was called the Son of God and the largest religious movement in human history is centered around his teachings; he was very likely a real person. EVEN IF this is all Jesus is, following his teachings can promote peace, empathy, and genuine morality.