I am currently taking a Philosophy class and I am reading different arguments for the existence of God. For example, so far we covered Aquinas, Descartes,and Spinoza. Are the arguments by these philosophers useful for Christians arguing for the existence of God? Granted that Spinoza did not believe in the Judeo-Christian God, he did nevertheless give an argument for the existence of God. Should Christians use these arguments for the existence of God? Do you know of other philosophers or theologians that give a fairly good argument for the existence of God?
It is hard to give an answer to your question which applies to every person you might share your faith with. For some people, arguments for the existence of God might be really key to helping them come to faith in God and becoming a Christian. However, there is a much greater number whose belief in God is not dependent on any sort of rational argument for or against the existence of God. My experience is that only a rather small percentage are swayed by such arguments. My answer is that such arguments can be useful in some cases. Thomas Aquinas felt that it was important to give a rational argument for the existence of the biblical God. Those who are fans of what is known as Classical Apologetics believe that these arguments are the basics for all Christian Apologetics. I am not one of those who believes apologetics must start there. In my opinion, evidence such as that from fulfilled messianic prophecies or rational arguments using the claims of Jesus or claims of miracles are more useful than logical arguments for God’s existence.
If you are interested in this topic, you should get access to a modern source on the existence of God which can give you a good summary, as well as more modern (and therefore more useful) versions of these arguments. A good summary is found in Philosophical Foundations for a Christian Worldview by J. P. Moreland and William Lane Craig. What you will find is that the arguments for the existence of God have not changed all that much over the past few hundred years. If you have read Aquinas, DesCartes and Spinoza, you are alreadyhave seen the main arguments, although the teleological argument has a much greater basis now than it did at the time of Spinoza, given the scientific discoveries since the seventeenth century.