My union with the Lord Jesus makes me know for certain translates “I know and I have been persuaded in the Lord Jesus.” The Good News Translation takes “I know” and “I have been persuaded” as an instance in which two verbs with similar meanings are used to strengthen one another, and hence the translation know for certain.
In other contexts the phrase “in the Lord Jesus” (see 6.3) would normally be taken with the meaning of (in) union with the Lord Jesus. Both An American Translation* (“as a follower of the Lord Jesus”) and the New English Bible (“as a Christian”) take it in this way. However, there are some who see a different meaning in the present context. Several translations take this phrase to mean “on the authority of the Lord Jesus” (New American Bible; footnote in New English Bible; see Jerusalem Bible “and I speak for the Lord Jesus”). Either of these interpretations is possible, though the meaning of “in union with the Lord Jesus” has stronger support on the basis of similar passages. There is little support for the exegesis reached by Phillips: “as in the presence of the Lord Christ.”
My union with the Lord Jesus may be understood as cause—for example, “because I am joined with the Lord Jesus, I know for certain that nothing is unclean of itself.” One may follow the lead of An American Translation* or the New English Bible in this type of rendering and translate as “since I am a follower of the Lord Jesus” or “since I am one who believes in the Lord Jesus.”
The term unclean is used purely in a religious sense of that which defiles the worshiper; this is in keeping with the use of this term both in the Old Testament and in other New Testament passages. The translation of the remainder of this verse is not difficult, but it may be helpful to explain what is meant by then it becomes unclean for him. What Paul means is that even though something may not be wrong in itself, if a man believes it is wrong and does it, then he commits a sin against his own conscience.
The term unclean in this context refers to something which may be said to have “negative taboo.” That is to say, it is excluded from everyday use because it would defile or make one impure. “Positive taboo,” on the other hand, is something which is so filled with “spirit power” that it is dangerous for the uninitiated or the unconsecrated to touch or deal with. Positive taboo, for example, was associated with Mt. Sinai, the covenant box (the ark), the temple, the holy of holies, as well as the vestments and the utensils employed in Jewish ritual. It is generally not satisfactory to translate unclean merely as “dirty” or “not clean,” since in most languages there is no relation whatsoever between dirt and defilement. A more satisfactory equivalent for unclean is usually an expression which means “to defile” or even “to make bad.” In fact, in some languages the only satisfactory term for unclean in this particular context seems to be a word with the general meaning of “bad” or “harmful”—for example, “there is no thing which, by itself alone, is bad; but if a man believes that something is bad, then it becomes bad for him to do it.” One must avoid in the use of a term for “bad” a meaning which would imply “inherently evil,” and thus suggest activities which are evil irrespective of circumstances, things such as murder, robbery, covetousness, etc.
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 .