Why do you say these things, when you know I will kill you for it?
As the Atlas of Middle Earth makes clear, it is not necessarily a contradiction to say that something is, for instance, “globed within the void” and “a flat circle” at the same time: the top could be a flat circle with a hemisphere of earth underneath it 
Aside: The first homework problem in one of my GR textbooks gives a map of Middle-Earth with distances between four of the cities, and then asks whether Middle-Earth is round or flat, and what its radius is.
Not close enough at all. That passage, which likens the heavens to a canopy or tent, is fairly clearly envisaging a flat Earth. At the time of Isaiah (8th century B.C., if Wiki is to be believed) the Greeks also believed the Earth to be flat; indeed, Anaximenes, the most advanced and “scientific” Greek thinker of his time still took this for granted in the later 6th century. I do not think it is known for sure who, among the Greeks, first made a convincing case for the Earth being spherical, but I have seen it attributed to Parmenides, in the early 5th century, who may have experimented with spheres casting shadows on one another to show that the shadow cast during a lunar eclipse was consistent with a spherical Earth (evidence for this is scanty, however).
In any case, by Aristotle’s time, in the 4th century B.C., it was clearly uncontroversial, amongst educated Greeks, that the Earth is a sphere (certainly Aristotle did not discover it for himself). Furthermore, well before Jesus’ time, the Eastern Mediterranean, including Palestine, had been thoroughly Hellenized, thanks to the conquests of Aristotle’s student, Alexander the Great, and it remained so even after the area was subsequently conquered by Rome. That is why the New Testament was written in Greek. That was the language of educated culture in the area at the time (although not the generally spoken vernacular). A well educated person in Jesus’ world would probably have known, thanks to his Greek education, that the world is spherical. The writers of the Gospels, and the rest of the New Testament, probably knew. Whether Jesus himself knew is another matter. He probably knew people who would have known, but who can say if the issue ever came up for him?