The original order of verses 4-5 is not certain; manuscripts dating from the second century differ in the order of presentation. The manuscript evidence, though rather certain, is not conclusive (the UBS Greek New Testament gives its choice of text a “B” rating). The argument that verse 5 may have been placed prior to verse 4 by an early scribe is suggested by the possibility that the scribe may have tried to make a type of antithetical parallelism between verse 3 (mention of heaven) and verse 5 (mention of earth). On the other hand, there seems to be no obvious reason for suggesting why he may have placed verse 4 before verse 5, had verse 5 originally come first, unless this was an attempt to place verses 3-4 together on the basis of their common background in Isaiah 61.1-2. Among the translations, New Jerusalem Bible, Bible de Jérusalem (Bible de Jérusalem), and Traduction œcuménique de la Bible (with a footnote) depart from the traditional order; New American Bible retains the order but places verse 5 in square brackets.
Those who mourn points in the same direction as the previous beatitude; taken together, verses 3 and 4 are an allusion to Isaiah 61.1-2.
“To comfort those who are mourning” is one of the promises of the anticipated Messianic salvation (see Luke 2.25). In the Septuagint the verb mourn is used both for mourning in behalf of the dead and for the sins of others. It is a common verb in biblical Greek and cannot be confined to the idea of mourning for sin. According to Matthew, one hates sin and forsakes it; one does not mourn it. In the present context the idea is best interpreted as a contrast between the “mourning” of the present age and the “comfort” of the coming age. At least this is highly probable in light of its connection with the words from Isaiah. Translators can show this contrast with a phrase such as “people who are mourning now (or, at this time).”
As we said, no reason for the mourning is given, nor should it be in the translation. If a language does require some kind of reason for the mourning, translators should try to be indefinite or use a phrase such as “because they need God.” This is not ideal, however.
It would have been immediately evident to any Jewish reader of Matthew’s Gospel that shall be comforted was merely a way of affirming the result of divine activity: “God will comfort them” (Good News Translation). Such a so-called “divine passive” construction was typical of Semitic language usage, and the theological outlook of Judaism expected that God himself would save and comfort his people. Comforted means “consoled” or possibly “made happy again.” Thus translations can have “God will restore their happiness” or “God will console them.”
Quoted with permission from Newman, Barclay M. and Stine, Philip C. A Handbook on the Gospel of Matthew. (UBS Handbook Series). New York: UBS, 1988. For this and other handbooks for translators see here .