If you are able to give the greek text you are looking at, it will help others answer your question. , 4καὶ ἡ οὐρὰ αὐτοῦ σύρει τὸ τρίτον τῶν ἀστέρων τοῦ οὐρανοῦ καὶ ἔβαλεν αὐτοὺς εἰς τὴν γῆν. καὶ ὁ δράκων ἕστηκεν ἐνώπιον τῆς γυναικὸς τῆς μελλούσης τεκεῖν, ἵνα ὅταν τέκῃ τὸ τέκνον αὐτῆς καταφάγῃ. First off, let me admit that this is my initial impression of this passage, and I may be off base as I am pulling only from my own relatively limited knowledge of greek grammar. This present seems to be functioning as a historical present. It is located in narrative material with a verb of action and is in the third person. The historical present only occurs in the third person, though it can occur as a singular or plural verb. In these types of passages, the context helps clarify the usage of the present. Since it is found here in narrative material, you instinctively knew the meaning even though you are unfamiliar with the usage. I believe most grammarians would say that it is used to emphasize some action or sequence, in this case perhaps the sweeping. I tend to view this construction as being similar to something an English speaker might say to his friends when describing some unusual or important event that happened to him. Maybe something like, " yesterday I had to pick up my car from the mechanic, so I went into the shop. No one was in the office so I walk up to the counter and ring the bell..." You would know that the event is clearly in the past, but the present is used to put the audience in the moment with you. It often seems to alert the reader that something significant is taking or is about to take place. That's my two cents, but you will probably receive a much better and more informed answer shortly.
Ἀσπάζομαι μὲν καὶ φιλῶ, πείσομαι δὲ μᾶλλον τῷ θεῷ ἢ ὑμῖν.-Ἀπολογία Σωκράτους 29δ