What exactly is Postmodernism? How does it affect the church and Christians?
Postmodernism was a sweeping movement that developed in the mid- to late 20th century, and touched on philosophy, the arts, architecture, and criticism, marking a full departure from modernism. Postmodernism is basically applied to the historical era which followed modernity. At its heart was a general distrust of all the great theories and ideologies of mankind. This great movement was characterized by a broad skepticism of everything, subjectivism rather than objectivism, or relativism. They had a general suspicion of reason. Accepted axiomatic truths and philosophies were the enemy. You could see Postmodernism as a rejection of intellectual assumptions and values that were prevalent in the “modern” society. Basically, it was a radical dose of skepticism given to a modern-day society. It was a worldview that was skeptical of everything. The tried and true conventions, morals, and ethics were rejected. Dr. Henry M. Morris wrote, “To the postmodern everything is relative. What may be true or right for one person may not be true or right for the next. Ethics is a matter of taste, and what’s right is merely a pragmatic question of what works” (Morris, p. 116). In came pragmatism. If it worked for most of the people most of the time, then it must be right. In the vacuum of the riddance of objective truth, there were now fluid and fluctuating viewpoints that deny the existence of absolutes. Strangely, by stating that they do not believe in absolutes, they have just given us one! They are absolutely sure there are no absolutes. It’s oxy-moronic, to be sure. 
Relativism and Postmodernism are bedfellows. They are closely related in the sense that truth is relative and not objective. To the relativist, the doctrine that knowledge, truth, and morality exist in relation to culture, society and historical context are not absolute. What might be true for you may not be true for me. It might seem wrong for you to do something that I may have no problem with, but there must be an order to our morals. If abortion is wrong, and the Bible makes it clear that it is wrong, it will always wrong, no matter what the culture says. Except for saving the life of the mother, abortion is murder, and it will always be murder, and that’s not subjective truth, but objective truth (Ex 20:13). It is not subject to personal or human interpretation. If everything becomes subjective, then everything suddenly becomes permissible. Truth becomes relative to the setting, culture, or circumstances, rather than what God says in His Word. Jesus is the Truth (John 14:6), and we are absolutely sure about that. Jesus Christ is the only way into the kingdom (Acts 4:12), and that was true then, it is true today, and it will be true forever. It won’t change with the culture or society or with the times. Relativism, much like Postmodernism, is a contemporary philosophy where there is no ready consensus on any one definition. For example, three witnesses at the scene of the accident might give radically different accounts since it’s relative to where they were standing when the accident occurred, however, all 3 saw the accident. There was an accident. They all agree on that. That is objective truth. There must be objective realities and truth, otherwise, with the absence of objective truth, we will all stumble into subjective error. The road to hell is paved with the best of intentions…subjective intentions. The road to eternal life is paved with objective truth; that God cannot lie and Jesus came to give His life as a ransom for many (Mark 10:45). Those truths are not negotiable, nor are they subject to interpretation. They are the truth!
Undoubtedly, the church has been affected by Postmodernism, and not in a good way. The “political correctness” police are everywhere. What was once a simple truth you could preach from the Bible can now suddenly be seen at “hate speech” in some nations (Like Canada for example), but if there is no objective truth (as postmodernists believe), then how can we believe anything…including the Bible!? The number of seminary graduates that believe in the inerrancy of the Bible is about 50% now. That means about half of all seminary graduates do not believe the Bible is perfect or without error! Let me say to these young seminary graduates who do not believe the Bible is the perfect Word of God: Get into another line of work! No preacher should ever preach who doesn’t believe in the Bible’s truthfulness! If only about half of the pastors in Protestant churches (51%) believe that the Bible is accurate, Jesus was sinless, Satan is real, God is omniscient, omnipresent, and omnipotent, that salvation is by grace alone, and we are responsible for evangelizing (Matt 28:18-2), then what of the other half that do not believe all these things? Why are they preaching? What damage are they doing to the people of God in those churches? Do they preach what they don’t believe?
Facts and Faith
Immanuel Kant, basking in the Postmodernism wave, created a divide of knowledge. On one side you have facts. On the other side you have faith, but Kant went so far as to say, “Facts have nothing to do with religion.” The Apostle Paul would disagree with that. He knew the resurrection a fact and that Jesus Christ was real. Those are facts and those are faith. Faith and facts are not incompatible. Paul said that he “delivered to you as of first importance what I also received: that Christ died for our sins in accordance with the Scriptures, that he was buried, that he was raised on the third day in accordance with the Scriptures” (1 Cor 15:3-4). Now “if Christ has not been raised, your faith is futile and you are still in your sins” (1 Cor 15:17). If people don’t believe these things, then they don’t believe the Bible. We know these things are true, because Paul wrote, that “in fact Christ has been raised from the dead, the firstfruits of those who have fallen asleep” (1 Cor 15:2). That is not a subjective truth; one of opinion or one that may change with the times; that is the unchangeable Word of God. It is objective truth, just as John 3:16 is!
Truth is negotiable today and that’s sad, because it is infiltrating the pulpit, and when there’s a mist in the pulpit, there’s a fog in the pew. People will follow just about anything or anyone. Remember, we are all like sheep, having been led astray (Isaiah 53:6). Jesus said that “many will come in my name, saying, ‘I am the Christ,’ and they will lead many astray” (Matt 24:4), but also, “many false prophets will arise and lead many astray” (Matt 24:11). By saying, “many,” we presume it’s not a few, and perhaps its most, but we know the truth and the truth has set us free. If not for the Good Shephard, we’d still be lost, but the truth is, Jesus came to give His life for us so that we might have God’s wrath removed from us and be seen as having Jesus’ own righteousness (2 Cor 5:21). But, those who reject the truth will finally discover the truth, but only after it’s too late (Heb 9:27; Rev 20:12-15).
Morris, Henry M. Defense of the Faith. Master Books, 1999.
Here is some related reading for you: What is the Emergent church? What do They Believe? 
Resource – Scripture quotations are from The Holy Bible, English Standard Version® (ESV®), Crossway Bibles. (2007). ESV: Study Bible: English standard version. Wheaton, Ill: Crossway Bibles. Used by permission. All rights reserved.