What I say is this is literally “but I say,” a common way by which Paul starts a section. In 3.17 and 4.1 such an expression is used to introduce a further explanation of a subject already under discussion. Here, as in Gal. 5.2, Paul uses it to get his readers’ attention to a personal appeal. In some languages an expression such as what I say is this would seem to be so self-evident as to be either meaningless or misleading. An equivalent expression may be “what I mean is this,” or “what I am trying to say is the following.”

Let the Spirit direct your lives is literally “walk by the Spirit.” Some take the Spirit here to mean spiritual life as opposed to “flesh.” Most translators, however, understand it as referring to the Holy Spirit. The verb “to walk” is frequently used in the New Testament in a moral sense, that is, as equivalent to “to live” or “to conduct one’s self.” The present tense of the Greek verb denotes action that is already in progress. Hence it can be rendered as “continue to walk.” The whole expression means that the Galatians should allow their whole life to be controlled, or regulated, by the Holy Spirit (Jerusalem Bible “guided by the Spirit”; also New English Bible). Let the Spirit direct your lives should not be understood merely as a kind of “permission.” The imperative form of the Greek text may be translated as “live in accordance with the way in which the Spirit tells you to,” or “… the way God’s Spirit directs you.”

The next clause in this verse has been interpreted as equivalent to an imperative (as in Revised Standard Version), but most translations employ a future indicative (as in Good News Translation). In the former case, it is an emphatic command; in the latter, it is a strong assertion that once they allow the Spirit to guide them, “then you will never satisfy the passions of the flesh” (Moffatt).

There are three words in this clause that need to be commented on: satisfy, desires, and human nature (literally “flesh”). Satisfy is literally “to fulfill,” but it is used here in the sense of “to gratify” (Revised Standard Version). Desires or “passions” refers to any kind of desires, both good or bad, but the New Testament usage points more to the bad. Human nature (“flesh”) is the same word used in verse 13, and refers once again to that part of human nature which does not submit to God. This is not easy to translate; there is danger even in the Good News Translation way of rendering it, since it makes human nature all bad, and all its desires evil.

In a number of languages there is no closely corresponding way to speak of human nature. The closest equivalent may simply be “you yourselves,” for example, “do not do just what you yourselves want to do.” In other languages one may say “do not do what you as a human being want to do,” or “… just as a person wants to do.” In still other languages human nature is best spoken of as “the heart,” for example, “do not do just whatever your heart wants you to do,” or “… just whatever you want to do in your heart.”

Quoted with permission from Arichea, Daniel C. and Nida, Eugene A. A Handbook on Paul’s Letter to the Galatians. (UBS Handbook Series). New York: UBS, 1976. For this and other handbooks for translators see here .