Faith helps me observe and understand the outside world. And be in awe of it. Thinking logically helps me understand myself internally. And avoids internal pitfalls. Both are equally needed to develop a mentally aware and sound mind.
... and this is coming from someone who has a mental illness. It's similar to medication and therapy. Medication works from the inside coming out, therapy works from the outside coming in. Both are essentially needed by the severely mentally ill, including myself. If I don't take my medication I become irritable, anxious, agitated, and if I don't have therapy I can get in a really bad mood, for several days. They both work in tandem together, like living a spiritual life and having stable thinking.