"For this purpose I was born and for this purpose I have come into the world--to bear witness to the truth. Everyone who is of the truth listens to my voice." Pilate said to him, 'What is truth?...'" (John 18:37-38 ESV)
One of the main problems in communicating with people today is a lack of clarity regarding what our standard of judgment is. What framework, what authority, does each of us see as ultimate and binding? When someone says, "what's wrong with ______ ", there is usually an implied basis for judgment. It may be what seems "reasonable", or its wide cultural acceptance, or some scientific study which seems to support it.
J. Gresham Machen notes, "The first question in dealing with any difference of opinion is the question what standard of judgment is to be applied to the question at issue." (The Christian Faith in the Modern World)
I drew the chart above with spheres of authority. God's Word is a solid circle; the others are dotted (fluctuating, variable). There are overlaps. This is to show that there are things in a culture which the Bible would affirm, as well as things the Bible would condemn.
Reason and science are helpful tools in gaining knowledge, but cannot be the basic determination of truth, especially ethical and spiritual truth. Reason is an important process, but by itself reason does not determine ultimate truth or ethical obligations. Science has many limitations, but true discoveries are true because God created this world for us to study and discover. However, science cannot tell us many things: purpose, meaning, what went before time, or after, or what is right and wrong. As one philosopher said long ago, "We are afloat on the raft of our knowledge upon the sea of our ignorance."
Likewise, our friends, traditions, feelings, and experiences may help us to know some aspects of truth and to act well, but they are not the infallible authority regarding truth and goodness.
Again, Machen: "If we take the Bible as the Word of God, then the Bible becomes our standard of truth and of life. When we are asked whether we can support any kind of message or can engage in any course of conduct, what we do is simply to compare that message or that course of conduct with the Bible. If it agrees with the Bible, we can support it or follow it; if it does not agree with the Bible, we cannot support it or follow it no matter what we may be told by other authorities to do. Our standard is not a flexible standard. Far from holding that what is true today becomes false tomorrow according to the shifting needs of human life, we find our standard both of truth and of conduct in the Bible, which we hold to be not a product of human experience but the Word of God." (The Christian Faith in the Modern World)
Which leads me to examine another question: what is your (and my) operating -- or functional -- authority? I think many Christians would say that their authority for faith and behavior is God and his Word. However, for many that may be only in a formal sense. Is that so in a functional way? It is not enough to say that we believe God's authoritative Word, but then make actual decisions in life based upon feelings, experiences, friends' opinions, polls, what "makes sense", or what the culture approves.
In making daily ethical choices -- and in our conversations with others -- the Scriptures must be our authority, both in a formal and in a functional sense.
"To the law and to the testimony! If they do not speak according to this word, they have no light of dawn." (Isaiah 8:20 NIV)