If Christ be not risen. — Better, but if Christ be not raised; and so all through this passage.
Then is our preaching vain, and your faith is also vain. — The Apostles had preached a risen Christ, their converts had believed in a risen Christ, but now the proposition is, There is no resurrection; therefore Christ is not risen; therefore the preaching and the faith which are based on the delusion that He is risen are both vain and useless. The argument is still purely an appeal to historical evidence supporting an historical fact, and to the consequences involved in denying that fact (see 1 Corinthians 15:16).