... In the days of R. Yehoshua ben Chananiah the evil kingdom (Rome) decreed to rebuild the Temple. Papos and Lulianos (two brothers who were later martyred in Lod) set up tables from Akko to Antioch and supplied the pilgrims from the diaspora with silver, gold and all of their needs. Some Kuthites went [to the emperor] and said, "The king should know that if this rebellious city is built and its walls fortified, 'they will not pay tribute, poll-tax, or land-tax.'" He said to them, "What should I do, I have already made the decree?" They said to him, "Send to say to them [that] they either change the place of the Temple or add or remove five ells from it and they will recant on their own." And all of the [Jewish] people was gathered in Beit Rimon. When the king's edict arrived, they began to cry. They sought to rebel against the king. [The sages] said, "Let a wise man go up to quiet the assembled." They said, "Let R. Yehoshua ben Chananiah go up, as he is learned in the Torah." R. Yehoshua ben Chananiah went up and expounded, "A lion was devouring prey [and] a bone got stuck in its throat. It said, 'I will give a reward to anyone who comes and removes it.' An Egyptian heron with a long beak put his beak into the mouth of the lion and extracted the bone. It said to the lion, 'Give me my reward.' The lion said to it, 'Go and praise yourself, "I went into the mouth of the lion in peace and I came out in peace" - and there is no greater reward than that.' So too, it is enough for us that we entered into this nation in peace and came out in peace"...
Hadrian's offer was rebuffed by the Jews who viewed this decree as a sacrilegious. As it goes, however, Hadrian still had his city built, a temple to Jupiter Capitolinus errected, issued a ban on circumsicion, and placed a heavy tax on Jews in Palestine.
This then brings us to the Epistle of Barnabas:
I will also speak with you concerning the Temple, and show how the wretched men erred by putting their hope on the building, and not on the God who made them, and is the true house of God. For they consecrated him in the Temple almost like the heathen. But learn how the Lord speaks, in bringing it to naught, "Who has measured the heaven with a span, or the earth with his outstretched hand? Have not I? saith the Lord. Heaven is my throne, and the earth is my footstool, what house will ye build for me, or what is the place of my rest?" You know that their hope was vain. Furthermore he says again, "Lo, they who destroyed this temple shall themselves build it." That is happening now. For owing to the war it was destroyed by the enemy; at present even the servants of the enemy will build it up again.
Some interpret this passage as an anachronism about the building of the second Temple. However, the text makes it clear that the ones who destroyed the Temple are the ones who shall rebuild it. The Babylonians destroyed the Temple, while the Persians allowed the Jews to rebuild it. So it cannot have been about the second Temple. Still others assume that the passage is referring to a "spiritual Temple," and while the Epistle does speak about such a Temple throughout, I believe that this is acknowledging the construction of a real, physical Temple. The context assumes such a reading.
And here we have a definitive date range for the Epistle, as it was the Romans who destroyed it during the war of 70 ad, and now it is Hadrian, a Roman emperor, who shall rebuild it. "Lo, they who destroyed this temple shall themselves build it". This places the Epistle ca. 125 ad.
But could the Epistle of Barnabas be Marcionite? There are circumstantial reasons to assume so. It's emphasis that the rites, laws and customs of the Jews have been made obsolete by Jesus Christ (so named in the Epistle) is Marcionite, and how it characterizes the Jews as wretched and as no better than the heathens is also a Marcionite stereotype. It also, like Paul, Marcion's favourite Apostle[*], relies on Jewish prophecy and scripture to clarify it's meaning that this was divinely orchestrated by God, for both Jews and Gentiles alike. But what does it mean by God?
In discussing the rite of baptism issued by Christ, the Epistle writes,
"And again the Prophet says, 'I will go before you and I will make mountains level, and I will break gates of brass, and I will shatter bars of iron, and I will give thee treasures of darkness, secret, invisible, that they may know that I am the Lord God.'"
The treasures spoken of is strongly suggestive of the true God of Marcion, a god who is removed, absent, remote, secretive, and invisible. That the author is quoting a passage about the figure of Cyrus is all the more conspicuous, as it was Cyrus who was anointed by YHWH and who allowed the Jews to return to their homeland.[**] Everything in the Epistle indicates that it is the god of the Jews who he is invoking.
There is nothing at all strange or enigmatic about this. Jewish scriptures, time and again, states how the Jews are a wicked people when they reject their god, and such an indictment in the Epistle is in keeping with that. Lest a certain someone claims that Marcion and the Epsitle reject Judaism and YHWH respectively, the argument is disproved on the outset.
* It is my opinion that Paul and Marcion are in fact the same individual.
** It is possible though not at all absolutely provable that the writer of the Epistle of Barnabas is comparing Hadrian to Cyrus. Hadrian was also given the title of κύριος, and the author would have been acutely aware of the connection as κύριος was a title for YHWH as well.