Theologian? What's a theologian?
Any Christian who thinks about God, his ways and his glory is a theologian. If we have or are seeking answers to questions like, Who is God? What is he like? Who are we? Who is the Holy Spirit? and so on, we are theologians.
It would be a wonderful thing if every Christian could work out, and then speak out (or in the rare cases where they are interested in writing, write out) their own answers to these questions to another believer, or to a small group.
But as each of us work out our "theology", we need to....
(1) Know the thinking / philosophy of your own age. In other words, understand where your particular age is coming from, know its worldview. Why? Because we are shaped much more by our worldviews than we ever imagine. Example? I came across an author recently who called interpreting the Bible a "science", he said something like "hermeneutics is an exact science." He was probably unaware that he was speaking the language of the Enlightenment, and its daughters 'modernism' and 'science'. He was sure that he was just being Biblical but in fact he was deeply influenced by the worldview he grew up in called "modernism". How will you be able to detect whether or not you have absorbed the spirit of your age unless for a moment you try to stand outside of it and ask what your school teachers and TV bosses and newspaper editors believe?
(2) Know what your own theological 'tradition' is. Every one of us come from a particular theological tradition, whether it be reformed, brethren, Presbyterian or charismatic. We must consciously explore it, and try to assess its strengths and weaknesses. No 'tradition' is perfect, shaped as it is by many different influences. (Unless of course we think we come from the perfect tradition - which some people believe). It is actually helpful to read other traditions to give us some kind of perspective, even though we may not in the end agree with them. (Unless you find yourself in a denomination who alone has the truth).
(4) Do your theology in community. What do I mean? The church, not an individual in his or her study, is the pillar and ground of truth. If you pursue truth on your own, it will be 'you-shaped'. If you are one of those laid-back characters, your theology will be a little wishy washy. If you are one of the zealous narrow-minded types, your theology will be narrow and judgmental. Only by discussing what you believe within the body will you get Christ-like perspective.
(5) Beware of taking human logic further than Scripture. We all must use our minds to work things out, but herein lies a great danger: theology can be dangerous. Human reason can so easily go one step further than Scripture. For example, we might reason from Genesis 3 that Adam and Eve's sin was the first time God was ever grieved. How do we know that? It is purely a logical extension from the text. There is no verse to say that God was never grieved by sin before this. I mean what about the fall of Satan? Human reason tries to systematise truth and tie up every loose end - a real danger to watch out for.
(6) Be certain where you can.... On many central themes of Scripture, we can say "we know this for sure". We know that God is Three in One. We know that Jesus Christ is both human and divine. We know that salvation comes to us by faith alone - and so on. These central truths can be easily worked out from the following: (i) how often a truth is mentioned in Scripture (we know God created the universe and us, because it says so frequently in Scripture), (ii) whether a truth is said to be central (for example in 1 Corinthians 15, Paul says that the Resurrection is central), (iii) whether a doctrine is essential to salvation (again, the Resurrection is an example). We might also add (iv) do orthodox Christians in history recognise this doctrine as a must? Is it in the Apostle's Creed, the Nicene Creed, and so on.
(7)....remain open where you must. After being sure where you can, remain open where you must. To remain open is to acknowledge that there are secondary truths, on which Christians disagree. By secondary we do not mean unimportant, we simply mean that Christians in all ages have disagreed about them. For some reason the Holy Spirit has not seen fit to make them so manifest that every Christian sees it in the same way. The details of Christ's return are an example. All Christians believe he is returning, but exactly how, they disagree. This example sheds light on the larger picture. You will find that to every primary doctrine (on which all Christians agree), a number of secondary doctrines are attached (on which Christians disagree). Learn to put secondary doctrines "on the shelf" and say to yourself "although I hold such and such a view presently, I may change my mind at some later stage. And I shall not judge my brother or sister who think differently."
(9) Make sure your theology is practical. The end of all theology is to know God and glorify him in our lives. If you cannot write a "so what" after a doctrine, question its value. Tragically some Christians think that being near the highway of truth is the same as being on it.
(10) Remember that knowledge puffs up but love builds up. There is nothing more unpleasant or more useless in the kingdom of Christ than a proud Christian, who, because they know stuff, exalts himself or herself above others. The greatest is not knowledge but love. One of Satan's crudest weapons (but such is the ignorance of his schemes, one of the most frequent weapons) is to hide pride behind knowledge and to divide believers over secondary doctrines.
(11) Jesus and his Gospel is the centre - and end - of theology. If Jesus Christ, who is the wisdom of God, and his Gospel which is the heart of the Bible, does not figure in all our theology, something is wrong with it. If our theology does not lead to Jesus and our deep need of his cross, if it does not make us like him in his character, full of grace and truth, it is dross not gold.
If in the end, theology is purely a mind exercise which does not lead us to Jesus Christ, it is of no more or less value than any other 'ology' or 'ism'.