Biblical argument for substance dualism
I do think a Biblical case can be made against substance dualism, but that case is not air-tight. Many of the passages (e.g. Ecclesiastes 9:5) could just as easily be used to build a case against resurrection. Some (e.g. Jehovah's Witnesses) are able to bring up dozens of passages showing that the word "soul" refers to any personal being, not to an immaterial self. They'll say we don't have a soul; we are one. But the words for soul and spirit are used in a variety of ways in the Bible, and they are arguably used to refer to the immaterial self in some passages.
There may be several places in the Bible that support substance dualism, but the case for substance dualism from those passages is not air tight. It's possible to interpret them in a way consistent with denying substance dualism. For example, some people use the parable about the rich man and Lazarus to argue for substance dualism, but this passage can be taken as a parable used by Jesus with no intention of explaining the reality of "life after death."
But there is one passage I think is about as air-tight as it's possible for a theological argument to be. 2 Corinthians 5:6-8 says,
So we are always confident, knowing that while we are at home in the body we are absent from the Lord. For we walk by faith, not by sight. We are confident, yes, rather to be absent from the body and to be present with the Lord.If we do not have an immaterial self that survives the death of the body and is capable of disembodied existence, then how is it possible to be "absent from the body" while at the same time being "present with the Lord"? I don't think it is possible, so it seems clear to me that Paul is assuming substance dualism.
I'm not about to say that some possible answer couldn't be given to this argument. Though I have yet to hear one (i.e. one that doesn't ignore my point), I've been sitting here trying to think of one myself. I suppose a person could argue that by being "absent from the body," Paul is referring to the present body, and that by being "present with the Lord," he's referring to when we recieve our future resurrection bodies. After all, in chapter 5, Paul does use some phrases similar to phrases he uses elsewhere in reference to resurrection. For example, in verse 2, he says, "we groan," which is similar to what he said in Romans 8:23: "we ourselves groan within ourselves , eagerly waiting for the adoption, the redemption of our body." In verse 3 and 4, he talks about being clothed so that "mortality may be swallowed up by life," which is similar to 1 Corinthians 15:53,54, which says "this mortal must put on immortality," so that "death is swallowed up by victory." That whole passage in 1 Cor 15 is about the nature of resurrection.
Suppose, though, that the Bible is completely silent on the topic. Couldn't we still draw some conclusion through philosophical reasoning? The philosophical case for some form of substance dualism seems strong to me, which is why I'm a substance dualist.