It's a very common mistake to make; thinking that atheist haven't read the bible. Most of us Western atheists were brought up Christian and chanted the bible like everyone else. I know it probably as well as most non fundamentalists do.
And I'm afraid there's no getting away from it, these are two connected sentences, one following the other, the second re-inforcing the first. To make it say anything different is simply retrofitting an excuse for the failed prophesy.
For the Son of Man is going to come in his Fathers glory with his angels, and then he will reward each person according to what he has done.
I tell you the truth, some who are standing here will not taste death before they see the Son of Man coming in his kingdom.
You are incorrect in your thinking because less than one year later, we find Jesus sitting upon the Mount of Olives, again in private conversation with his disciples.
Jesus explains what the sign of his future presence will be and then warns: Keep on the watch, therefore, because you do not know on what day your Lord is coming.
His followers must be constantly alert because the time of his coming is unknown. They must be ever ready for it.Matthew 24:42.
In the manner of his coming, the Lord resembles a thief. He goes on to say: But know one thing, that if the householder had known in what watch the thief was coming, he would have kept awake and not allowed his house to be broken into. (Matthew 24:43)
A burglar does not make an announcement informing the householder when he will strike; his main weapon is surprise. Therefore, the householder must be on constant guard. However, for the faithful Christian, unflagging vigilance is not due to any fearful apprehension. Rather, it is motivated by an eager expectation of Christs coming in glory to usher in his Kingdom rulership.
Despite all the watching, no one will ever figure out in advance the exact day he is due to come. Jesus says: On this account you too prove yourselves ready, because at an hour that you do not think to be it, the Son of man is coming. (Matthew 24:44)
If a Christian were to think that on a certain day, Christ would not come, perhaps that would be the very day that he did come! Of course, well-meaning, faithful Christians in the past have sincerely tried to predict when the end would come of this present system Yet, Jesus caution has been proved true time and time again: Concerning that day and hour nobody knows, neither the angels of the heavens nor the Son, but only the Father.Matthew 24:36.
As we see that the transpiration was seen by three of his disciples, marking the Kingdom arrangement as a future event, as we see later on, Jesus explained to them in further detail, what they had to do and why.