The letter of Barnabas is not canonical having misunderstandings and misinterpretations in it. Neither today is it believed to have been written by the Barnabas who accompanied Paul but rather by another Barnabas in Alexandria. There are two clues to its date. Firstly there is Chapter 16 where the write 'Barnabas' considers the temple saying..
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.
2 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. [Isaiah 40:12] 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?" [Isaiah 66:1]You know that their hope was vain.
3 Furthermore he says again, "Lo, they who destroyed this temple shall themselves build it." [LXX Isaiah 49:17]
4 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.
5 Again, it was made manifest that the city and the temple and the people of Israel were to be delivered up. For the Scripture says, "And it shall come to pass in the last days that the Lord shall deliver the sheep of his pasture, and the sheep-fold, and their tower to destruction." [1st Enoch or Ethiopian Enoch 89:56] And it took place according to what the Lord said.
6 But let us inquire if a temple of God exists. Yes, it exists, where he himself said that he makes and perfects it. For it is written, "And it shall come to pass when the week is ended that a temple of God shall be built gloriously in the name of the Lord." [1st Enoch or Ethiopian Enoch 91:13]
7 I find then that a temple exists. Learn then how it will be built in the name of the Lord. Before we believed in God the habitation of our heart was corrupt and weak, like a temple really built with hands, because it was full of idolatry, and was the house of demons through doing things which were contrary to God.
8 "But it shall be built in the name of the Lord." Now give heed, in order that the temple of the Lord may be built gloriously. Learn in what way. When we received the remission of sins, and put our hope on the Name, we became new, being created again from the beginning; wherefore God truly dwells in us, in the habitation which we are.
9 How? His word of faith, the calling of his promise, the wisdom of the ordinances, the commands of the teaching, himself prophesying in us, himself dwelling in us, by opening the door of the temple (that is the mouth) to us, giving repentance to us, and thus he leads us, who have been enslaved to death into the incorruptible temple.
10 For he who desires to be saved looks not at the man, but at him who dwells and speaks in him, and is amazed at him, for he has never either heard him speak such words with his mouth, nor has he himself ever desired to hear them. This is a spiritual temple being built for the Lord (Barnabas 16 non canonical).
This shows us that 'Barnabas' considered Ethiopian Enoch to be canonical and quotes some fascinating scriptures. From verse 5 we see that Jesus will deliver the sheep from the Watchtower and destroy both their administration and their HQ and the position as bible interpreters (their metaphorical tower). Now verse 4 places the letter after the physical temple was destroyed in 70CE and before the Bar Kochba revolt in 132 after which there could be no hope that the Romans would help to rebuild the temple (wikipedia - Epistle of Barnabas - see also Studies in the Jewish background of Christianity - D. R. Schwartz). Since the Romans never did help rebuild the physical temple, and since in fact it has not been rebuilt to this day, Barnabas made an incorrect interpretation. But it was a good attempt (he did that a lot). He did understand that the fulfilment really was for a spiritual temple. Actually the people who knocked down the first true Christian church, TCC1, would help build the second TCC2. Likewise the JWs will help to build the LWs once the sower and the reaper start rejoicing together.
The second clue comes from chapter 4, referring to the 10 kings, we read...
3 The final stumbling block is at hand of which it was written, as Enoch says, "For to this end the Lord has cut short the times and the days, that his beloved should make haste and come to his inheritance."
[but no one can find this quote!]
4 And the Prophet also says thus: "Ten kingdoms shall reign upon the earth and there shall rise up after them a little king, who shall subdue three of the kings under one."
5 Daniel says likewise concerning the same: "And I beheld the fourth Beast, wicked and powerful and fiercer than all the beasts of the sea, and that ten horns sprang from it, and out of them a little excrescent horn, and that it subdued under one three of the great horns." (Barnabas 4 - non canonical)
[but no one can find this quote!]
So Barnabas was written before the rapture at the end of the first presence which we presently believe occurred in 123/124 AD.
Barnabas makes some good but incorrect attempts to explain the greater meaning of the law of Moses and of the twins in the womb of Rebecca...
Now let us see whether this people or the former people is the heir, and whether the covenant is for us or for them.
2 Hear then what the Scripture says concerning the people: "And Isaac prayed concerning Rebecca his wife, because she was barren, and she conceived. Then Rebecca went forth to enquire of the Lord and the Lord said to her: two nations are in thy womb, and two peoples in thy belly, and one people shall overcome a people, and the greater shall serve the less."
3 You ought to understand who is Isaac and who is Rebecca, and of whom he has shown that this people is greater than that people. (Barnabas 13).
Barnabas imagined that Jacob and Esau stood for the Jews and the Christians. He was not quite correct, they were not twins - see U51. But at least he recognised that the old testament is not a dead Jewish soap opera, but a living prophetic odyssey which foretells the future metaphorically in terms of the events of the past.
The big find in Barnabas is chapter 15, concerning the Sabbath, which says...
1 Furthermore it was written concerning the Sabbath in the ten words which he spake on Mount Sinai face to face to Moses. "Sanctify also the Sabbath of the Lord with pure hands and a pure heart."
2 And in another place he says, "If my sons keep the Sabbath, then will I bestow my mercy upon them."
3 He speaks of the Sabbath at the beginning of the Creation, "And God made in 6x days the works of his hands and on the 7th day he made an end, and rested in it and sanctified it."
4 Notice, children, what is the meaning of "He made an end in 6 days"? He means this: that the Lord will make an end of everything in 6,000 years, for a day with him means a thousand years. And he himself is my witness when he says, "Lo, the day of the Lord shall be as a thousand years." So then, children, in 6 days, that is in 6 thousand years, everything will be completed.
5 "And he rested on the 7th day." This means, when his Son comes [at the start of that day] he will destroy the time of the wicked one, and will judge the godless, and will change the sun and the moon and the stars, and then he will truly rest on the 7th day [Amen].
6 Furthermore he says, "Thou shalt sanctify it with clean hands and a pure heart." If, then, anyone has at present the power to keep holy the day which God made holy, by being pure in heart, we are altogether deceived.
7 See that we shall indeed keep it holy at that time, when we enjoy true rest, when we shall be able to do so because we have been made righteous ourselves and have received the promise, when there is no more sin, but all things have been made new by the Lord then we shall be able to keep it holy because we ourselves have first been made holy.
8 Furthermore he says to them, "Your new moons and the Sabbaths I cannot away with." Do you see what he means? The present Sabbaths are not acceptable to me, but that which I have made, in which I will give rest to all things and make the beginning of an eighth day, that is the beginning of another world/Eon [the 8th day of the previous week is the 1st day of the next week. There are 7 of these, the first 6 begin new 6,000 year working weeks, the last 8th day is the 50th day which is the Jubilee, which is the end of all Sabbaths. It is the 'day' when all of mankind become Gods!]
9 Wherefore we also celebrate with gladness the eighth day in which Jesus also rose from the dead, and was made manifest, and ascended into Heaven (Chapter 15)
So here we have the basis of the 6,000 year lease Satan has on this planet from the founding of the world on 3993Nisan14 to the end of the world on 2008Nisan14. The end of his lease in any event.