Christians, in general, seem to have widely differing views on the role of scripture in their religion. Some use only a few portions of the New Testament, some only the New Testament, some add a bare touch of the Old Testament, and some believe the Bible collection of scripture to be definitive. Still others accept all ancient books as part of scripture, and others have specific books they add as scripture.
As an LDS (Mormon), I believe as is stated in the 8th Article of Faith (which is a declaration of the LDS basic tenets):
“We believe the Bible to be the word of God as far as it is translated correctly; we also believe the Book of Mormon to be the word of God.”
In addition to this, we have and make use of Prophets who are called by God to preach in these days. The word of the Prophet is more important than scripture, as it is what God wishes to tell us now, not what we needed when the scripture was written. It should also be noted that the Prophets also ask us to not take any of it on blind faith, but to pray and ask God for ourselves if what was given is true.
I have had friends leave the church over this. They were directed towards seeming inconsistencies in what the Prophets have said, and decided that it meant that someone along the line wasn’t really a prophet.
The reason we need prophets is the same as in Jesus’ time. We, as a people, change. God does not change, but we change in what we need to be taught and reminded of by God. Polygamy is a good example – God gave us instruction on how some men would take more than one wife, to be kept as a very sacred and holy covenant between God and those involved. Unfortunately, some took advantage of that teaching and twisted it to their own ends, and that doctrine was taken away. No one in the LDS church now enters into plural marriage, even if the country the members live in doesn’t disallow it or it is acceptable culturally. Even if the Bigamy laws were repealed in the US tomorrow, God would not direct his people to enter into that covenant until they, as a people, showed they were ready. Considering divorce rates, we have a very long way to go before then.
Having a living Prophet is invaluable to us. Having that direct guidance from God, which we can confirm personally, helps direct us as a people in improving our homes and communities and preparing us for the time when Jesus will return in glory. Its not a dismissal of scripture, but building upon; having even more resources available to us in our quest to become more like Jesus.