Assurance is in essence both biblical and experiential, as are most doctrines. The Unction of the Holy Spirit is not just a mental thing, but an experiential thing, we experience the Holy Ghost teaching us, the knowledge and theological biblical confirmation comes afterwards. This is the difference between a teachable person and an unteachable one. Faith itself is an experience before the confirmation of that faith is given "Blessed are they who believe and have not seen".
Personally in my life it has gone both ways experience leads to understanding and study leads to experiencing God and His Love via the Spirit. Sometimes, God needs to send a talking Donkey to show us our errors, other times a simple word from scripture will do.
Good Post
@Blues State and welcome to the Forum.
To answer your question, I grew up in a fundamentalist background and am now opening up to the moving of the Holy Spirit in the supernatural, so I am kind of the opposite of your upbringing. For me, fundamentalism shut the door to Jesus and the divine revelation of the Spirit as it descended into textualism as opposed to vibrant faith.... The scribes began to dictate the experiences we were to have, But God has a way of reaching each of us in different ways. My supernatural experiences have been in the area of divine revelation primarily as the Holy Ghost has been my teacher, and with that there have been many supernatural events, where he has given me the unction to see deception even before i understand the full scope of the deception.... Do you understand this? It is in the realm of Spiritual warfare, and the wielding of the supernatural weapons of our warfare. (2 Corinthians 10:4-5) If I were to rely only on my theological knowledge i would be at a loss in this warfare, but if The Spirit is supernaturally working through me that warfare brings down strongholds.
God bless