And when it comes to understanding the scripture, how do we determine what is true?
Ideally, which is exteremely rare, it is the truth that Lord opens to man in enlightening his mind when he reads or hears the Word (provided a man looks to the Lord Jesus Christ, and the truth that he sees agrees with the essentials of the Word, and thus is not some phantasy). How otherwise could Peter recognize the Lord for the Son of Man? Most men, though, at best, acknowledge this heaving heard from others. But most of the most is accepting the opinion on the basis of the trust to authority. So, the Roman-Catholic, the Orthodox and even not a few Protestants accept the views which they are taught in schools, but do they really see from the Word from the Lord, whether the teaching of their church is aligned with the Word or not?
Here is an opinion about the role of the doctrine in explaining the Word:
"76. VIII
THE CHURCH IS FROM THE WORD, AND IS SUCH AS IS ITS UNDERSTANDING OF THE WORD
That the church is from the Word does not admit of doubt, for the Word is Divine truth itself (n. 1-4); the doctrine of the church is from the Word (n. 50-61) and through the Word there is conjunction with the Lord (n. 62-69). But doubt may arise as to whether the understanding of the Word is what makes the church, for there are those who believe that they are of the church because they have the Word, read it or hear it from a preacher, and know something of its sense of the letter, yet how this or that in the Word is to be understood they do not know, and some of them little care. It shall therefore be proved that it is not the Word that makes the church, but the understanding of it, and that such as is the understanding of the Word among those who are in the church, such is the church itself. The proof of this is as follows.
77. The Word is the Word according to the understanding of it in a man, that is, as it is understood. If it is not understood, the Word is indeed called the Word, but it is not the Word with the man. The Word is the truth according to the understanding of it, for it may not be the truth, because it may be falsified. The Word is spirit and life according to the understanding of it, for its letter if not understood is dead. And as a man has truth and life according to his understanding of the Word, so has he faith and love according thereto, for truth is of faith, and love is of life. Now as the church exists by means of faith and love, and according to them, it follows that the church is the church through the understanding of the Word and according thereto; a noble church if in genuine truths, an ignoble church if not in genuine truths, and a destroyed church if in falsified truths.
78. Further, it is through the Word that the Lord is present with a man and is conjoined with him, for the Lord is the Word, and as it were speaks with the man in it. The Lord is also Divine truth itself, as likewise is the Word. From this it is evident that the Lord is present with a man and is at the same time conjoined with him, according to his understanding of the Word, for according to this the man has truth and the derivative faith, and also love and the derivative life. The Lord is indeed present with a man through the reading of the Word, but he is conjoined with him through the understanding of truth from the Word, and according thereto; and in proportion as the Lord has been conjoined with a man, in the same proportion the church is in him. The church is within man; the church that is outside of him is the church with a number of men who have the church within them. This is meant by the Lord's words to the Pharisees who asked when the kingdom of God would come:
The kingdom of God is within you (Luke 17:21).
Here the "kingdom of God" means the Lord, and from him, the church."
So, if I understand the whole case correctly, the genuine doctrine has to be procured, provided it is seens from the Lord in the Word, that this doctrine is true, and correctly and soundly and even rationally explains the Word. And then the Word can be seen as to its various aspecs in the light of that genuine doctrine.