In a sense this verse is a conclusion to all that Paul has said throughout this chapter. He brings together two contrasts: the contrast between death and life, and the contrast between wage and free gift. The man who lives in sin receives what he has earned—death; but the believer receives God’s free gift—eternal life.
The principal difficulty in translating the first clause of verse 23 is that in so many languages sin cannot be personified as an agent which pays wages. The closest equivalent may be “when a man sins he receives the consequences, that is, death,” “the result of having sinned is death,” or even “because a man sins he will inevitably die.” The relationship between sin and death is essentially cause and effect, and in some languages this relationship is expressed idiomatically—for example, “the wages for the sinful heart is the death way.”
God’s free gift is eternal life may be slightly recast as “God freely gives eternal life” or “God causes people to live without end as a free gift from him.”
In union with Christ Jesus our Lord may be understood either as the means by which eternal life is made possible or as a qualification of the nature of eternal life, that is, life lived in union with Christ Jesus our Lord. These ideas are closely related, and it is doubtful if one can insist on any real distinction between the two in Paul’s mind. The conclusion of this verse is similar to that present in 5.21 and 6.11.
In some languages the most satisfactory translation of in union with Christ Jesus our Lord is “this means that we are in union with Christ Jesus our Lord” or “that is to say, we are closely bound to Jesus Christ our Lord.” It is also possible to treat this final phrase as an expression of means (as indicated above) and to render the phrase as “our living without end is possible, because we are in union with Christ Jesus our Lord” or “by being in union with Christ Jesus our Lord, we can live unendingly.”
Quoted with permission from Newman, Barclay M. and Nida, Eugene A. A Handbook on Paul’s Letter to the Romans. (UBS Handbook Series). New York: UBS, 1973. For this and other handbooks for translators see here .