Essentially, we are not to rest in any system of doctrine as a final infallible authority, but we are to rest in the Holy Scriptures alone as such. We do indeed have many final authoritative creeds, canons, councils and doctrines of the faith speaking of the things proclaimed in Scripture, but Scripture alone is our final infallible authority. Good doctrine simply outlines that which is already stated in the Bible as truth. Any doctrine that is stated must be backed up with Scripture, and in many cases, that Scripture backed up with other Scripture. Human logic and reason are tools given to us by God, but these tools must be used within the confines of Scripture. If we draw a conclusion using logic or reason, then that conclusion must be backed up with Scripture, otherwise it is a humanly derived thought (don’t forget that our thinking has been corrupted by sin). If a theological truth is in one place of the Word, then it will be in other places. The authors of Scripture never contradict the other authors, because it is all God inspired (2 Timothy 3:16-17), and infallible. And if it is all God inspired, then none of it contradicts another part, because God does not contradict Himself. He is reality and He defines all things in all manners of life. And the Bible is His word to us about Himself and His glory, how we’ve fallen short of it, and how Christ has made purification for sins on the cross. If there is a thought about God, salvation, or man (for example) that cannot be backed up with or found in Scripture, then it is to be cast away as either non-truth or mere human speculation into that which has not been stated. What can be known about God, namely, His eternal power and divine nature, has been clearly revealed to everyone for all time in what has been made (Romans 1:19-20), but more specifically, He has revealed Himself to us in His Son Jesus (Hebrews 1:1-4), revealed in the pages of the Bible. We must go where Scripture goes and we must stop where Scripture stops. If we chop out certain truths about God and ourselves from Scripture (such as His wrath, election, our sin, hell, etc.) or manipulate Scripture to make it fit what we want it to say, then we are denying attributes about Him and ourselves that are essential to knowing the truth. If we add to what Scripture says, we are doing the same thing, just on the flip side of the coin, and we will not know Him truly, as He actually is. If we do not know Him truly, then we believe lies about Him being spread around by Satan to blind the minds of unbelievers (Ephesians 2:1-2, 2 Corinthians 4:3-4).