"Raised" here is an idiom for "caused to live again." This can be stated in active form. Alternate translation: "God has raised Christ from the dead" (See: [[rc://en/ta/man/jit/figs-activepassive]] and [[rc://en/ta/man/jit/figs-idiom]])
Here "firstfruits" is a metaphor, comparing Christ to the first of the harvest, which would be followed by the rest of the harvest. Christ was the first to be raised from the dead, and all who believe in him will also be raised from the dead. Alternate translation: "dead, like the first part of the harvest" or "dead; he is like the first part of the harvest" (See: [[rc://en/ta/man/jit/figs-metaphor]])