The Bible informs our systematic theology and only then our practice

"Having completed an Exposition of the whole Bible, the Books both of the Old and of the New Testament; I considered with myself what would be best next to engage in for the further instruction of the people under my care; and my thoughts led me to enter upon a Scheme of Doctrinal and Practical Divinity, first the former and then the latter; the one being the foundation of the other, and both having a close connection with each other." - John Gill, Body of Divinity, or Systematic Theology, Pg. 23