Hi Bill. My professor was not an atheist or agnostic – he was a friendly religious liberal who was heavily influenced by the teachings of Alfred North Whitehead (process theology), and he challenged our belief in what he called the traditional understanding of God, as well as the reliability and authority of the Bible. He described his understanding of God as “panentheism” – kind of a mix of pantheism (all is God) and theism. As part of that he would tell us that God is omnipotent, but not in the way we thought he was. For him that meant that God only had the power of persuasion, and that there was no guarantee that he would ultimately win out over evil. Further, God (god?) is caught up in evolution like everything else – but (I guess) just ahead of us.
How did I respond? Well, first I had to do a lot of extra reading (mostly Geisler’s books about the authority of Scripture), and I had to lean on my apologetics mentors (the late Bob and Gretchen Passantino) in order to know what to say and how to present it. More specifically, I didn’t debate my professor philosophically very much about his weak view of God, but rather I went to what I considered the source of his confusion: his weak view of Scripture. In fact, after lots of research and preparation I partnered with the university’s InterVarsity chapter, and spoke for two of their large group meetings in which I publicly challenged this professor’s views – knowing he had already confused a lot of students.
I should add that I went to his office ahead of time, told him what I was going to do, and invited him to attend. He came to at least one of those meetings, but I don’t think he liked it very much. That was okay – it seemed to help a lot of my fellow students. (And to be clear, I treated him with respect while challenging the things he was trying to teach us.)
You asked how I would respond differently today. I don’t think I would do anything very different – other than having a lot more information to wield after many more years of study. Then and now I viewed the truth about the Bible and about God as life-and-death matters that need to be studied in a very diligent and sober-minded way (see: John 8:32).