Cornelius Van Til was a controversial figure in his lifetime, and he remains controversial. Much of the controversy swirls around the correct interpretation of his views. What, if anything, is the enduring value of his work?
i) Both believers and unbelievers take many truths for granted. It's useful, especially in apologetics, to consider all the other things that must be true for any particular thing to be true. What must reality be like for your fundamental beliefs about the possibility of morality, modality, knowledge, induction, human significance, &c., to be warranted?
For instance, apostates commonly lose their Christian faith, but retain many residual beliefs that are inconsistent with atheism. They didn't stop to consider how many of their fundamental beliefs were implicitly grounded in God's existence. They fail to ask what's a necessary condition for their belief to be possible.
Or they do it backwards. They begin by rejecting God. Then cast about for some alternative to ground their fundamental beliefs. But if they don't have the answers in advance, then their apostasy was intellectually premature.
ii) It's possible not only to argue for Christian theology, but to argue from Christian theology. That's not viciously circular, because some Christian doctrines have independent explanatory value. It's not necessarily an argument from biblical authority to appeal to Christian doctrine. Rather, you can show how some Christian doctrines make better sense of what we must believe than secular alternatives.
iii) Apropos (ii), philosophy and theology overlap. It's a mistake to separate the two.
iv) In apologetics we attempt to find common ground with the unbeliever. But sometimes it's necessary to challenge their tendentious or arbitrary rules of evidence (e.g. methodological atheism).
v) If Christian theism is true, then mind is prior to matter. Reality is ultimately personal rather than impersonal. And that has greater explanatory value than physicalism.
vi) Van Til's rationalist/irrationalist square of opposition is useful.