"as it is, Christ" or "this is the truth: Christ"
"Firstfruits" here is a metaphor, comparing Christ to the first of the harvest, offered to God. AT: "the first to be celebrated as if he were harvested from death." (See: rc://en/ta/man/translate/figs-metaphor).
"Raised" here is an idiom for "caused to live again." This can be stated in active form. AT: "God has raised Christ, who is the firstfruits of those who died" (See: rc://en/ta/man/translate/figs-activepassive and rc://en/ta/man/translate/figs-idiom)
The abstract noun "death" can be expressed with the verb "die." AT: "people die because of one man" (See: rc://en/ta/man/translate/figs-abstractnouns)
The abstract noun "resurrection" can be expressed with the verb "raise." AT: "people are raised from the dead because of another man" (See: rc://en/ta/man/translate/figs-abstractnouns)