The book of The Acts, then, was written by a companion of Paul. That fact stands firm, even apart from any tradition. And that is the really important fact. If the book was written by an eyewitness, the particular name of the eyewitness is comparatively unimportant. But the tradition as to the name is without doubt correct. There is not the slightest reason for calling it in question. What the book of The Acts itself says about its author fits exactly what Paul says about Luke.
The authorship of The Acts is certain. The date, however, is not so clear. The book was written by Luke. But when was it written? The latter question cannot be answered with perfect precision. At least, however, since the book was written by Luke, it must have been written during the lifetime of a companion of Paul. A. D. 100, for example, would be too late, and A. D. 90 would be unlikely. A good deal can be said for putting the date at about A. D. 63. This early date would explain the abrupt ending of the book.
One of the most curious things about The Acts is that the narrative is suddenly broken off just at the most interesting point. The trial of Paul is narrated at very great length, but we are not told how it came out. The final decision, the climax of the whole long narrative, is just at hand; but with regard to it we are left altogether in suspense. Was Paul released? Was he condemned and executed? The author does not say. His silence requires an explanation.
The simplest explanation would be that Luke wrote his book at the very point of time where the narrative is broken off. Of course he could not tell us any more if nothing more had happened. He brought his narrative right up to date. Nothing more was possible.
It is true, other explanations may be proposed.
(a) It has been suggested, for example, that The Acts closes so abruptly because the author was saving something for another work. As The Acts is the continuation of the Gospel of Luke, so a third work, it is said, was planned as the continuation of The Acts. But even so, it seems rather strange that the author should not have given at least a hint of the outcome of that trial in order to take the edge off our curiosity. He has done something like that at the conclusion of his Gospel; why not also at the conclusion of The Acts?