I remember many years ago when I was a graduate student at Duke University, I had to meet someone in the biological sciences library. While I waited, I leafed through some scientific journals and began to read whatever caught my eye. I had a very difficult time understanding what I was reading because I was not familiar with the language of biology; although I did know some basic terms from my very limited study of biology, such as osmosis, metamorphosis, and fission. But the language of biology is much larger than scientific terms. It includes the meaning of those words and how those words are employed.
The point is that if one wants to understand biology in a substantive way, one has to learn the language. At first glance this may seem to complicate the matter, but in actuality the language of a discipline makes it simpler. The word "osmosis" can be used in discussion instead of having to explain what it is every time someone wants to refer to it. If there were no special biological verbiage, a two hundred-page textbook on biology would more than triple in size, which is probably a conservative estimate. So the unique language of a subject simplifies its discussion. But in order for that language to be useful, the terminology must be understood.
The same is true with theology. Christianity has its own language, and believers use it all the time in worship, Sunday school, and in the seminary classroom. We speak of Jesus as the Messiah, and we talk about the forgiveness of sins, grace, sin, judgment, and resurrection. We refer quite frequently to Jesus as Lord and Savior. Learning the language of theology is essential if it is to be understood.
The early Christians understood this necessity of language and the faith because it is not only necessary that we speak of God, but it is also critical that we employ our God-talk in the right way. When the bishops of the church gathered together in the town of Nicaea in 325 A.D., at the church's first ecumenical council to discuss the person of Jesus, they knew all too well that it was important that Christians speak correctly of Jesus. There were those in the majority, particularly in the West, who affirmed Jesus as God come in human form to save humanity. Others, especially in the East, claimed that Jesus was not divine, but the man whom God chose to bring salvation to the world. Both sides used Scripture to support their positions.
The church could have left the argument alone, saying that in actuality it did not matter whether or not Jesus was divine, but they knew better, for the debate had to do with idolatry. If Jesus was not divine, then it was idolatrous to claim as much, for only God deserves worship, and there was a whole lot of Jesus worship taking place in the early days of the church. But if Jesus indeed was divine, then to deny that truth was also idolatrous, for it would lead to a rejection of the worship of one who must be so adored.
The church (I would like to think) in its divinely inspired wisdom, officially decided the matter in favor of true incarnation, that is, God becoming truly human in Jesus Christ. The claim that Jesus is divine is part of the necessary language of Christianity that needs to be learned. Without the knowledge of this language, it is difficult to understand why it is that Christians do not also agree on the kind of language to use in discussing the faith, nor are they always unanimous on how to define those terms. So learning doctrine, the language of theology, is the only way Christians can carry on the discussion necessary to understand our differences and hopefully come to some agreement and, at the very least, an understanding of one another. Doctrine is the language of our faith that we need if we are to talk about that which we believe, even with those who dissent from the language as it is traditionally employed.
This is why doctrine is necessary.