That was an extremely distorted way to respond to this question. Any reader unfamiliar with the topic would conclude that Copernicans were convinced by theology that stars were massive. I’m sure this is not how you intended your statement to be interpreted.
Because the observors of the time, even those with the keenest eye sight, literally had a consistent perception of stars having a diameter… which had more to do with atmospherics than reality.
The perception of stars having diameter was so vivid and persistent, the belief continued on well into the 1700’s. Here is a wiki article discussion on the science of stars having perceived diameter from the viewpoint of an Earthling:
" Tycho had determined that a typical star measured approximately a minute of arc in size, with more prominent ones being two or three times as large.[10] In writing to Christoph Rothmann, a Copernican astronomer, Tycho used basic geometry to show that, assuming a small parallax that just escaped detection, the distance to the stars in the Copernican system would have to be 700 times greater than the distance from the sun to Saturn. "
“Moreover, the only way the stars could be so distant and still appear the sizes they do in the sky would be if even average stars were gigantic—at least as big as the orbit of the Earth, and of course vastly larger than the sun.”
"(As a matter of fact, most stars visible to the naked eye are giants, supergiants, or large, bright main-sequence stars.) And, Tycho said, the more prominent stars would have to be even larger still. And what if the parallax was even smaller than anyone thought, so the stars were yet more distant? Then they would all have to be even larger still.[11] Tycho said:
“Deduce these things geometrically if you like, and you will see how many absurdities (not to mention others) accompany this assumption [of the motion of the earth] by inference.”[12]
"Copernicans offered a religious response to Tycho’s geometry: titanic, distant stars might seem unreasonable, but they were not, for the Creator could make his creations that large if he wanted.[13] In fact, Rothmann responded to this argument of Tycho’s by saying:
“[W]hat is so absurd about [an average star] having size equal to the whole [orbit of the Earth]? What of this is contrary to divine will, or is impossible by divine Nature, or is inadmissible by infinite Nature? These things must be entirely demonstrated by you, if you will wish to infer from here anything of the absurd.”
This thread continues to abound with ironies.
Copernicus appeals to religious principles - - not because the religious ideas were what convinced him that stars were massive. He uses religious interpretation to as the last remaining rationalization for why giant stars should not be seen as an impediment.
On the other side of the issue, Tycho also resorted to religious defenses … but in a qualitatively different way:
“Religion played a role in Tycho’s geocentrism also—he cited the authority of scripture in portraying the Earth as being at rest. He rarely used Biblical arguments alone (to him they were a secondary objection to the idea of Earth’s motion) and over time he came to focus on scientific arguments, but he did take Biblical arguments seriously.[15]”
While Copernicus lands a perfectly solid counter-jab (by asking what is it about massive stars that you find to be impossible), Tycho seriously believes Biblical texts about the immobility of the Earth are sufficient grounds to reject a heliocentric model!
The similarities to our own little discussion groups here is amusing similar! While Creationists argue that the Biblical text argues against Evolution, @swamidass and I argue (and I believe more credibilty) there is no logical or theological reason for Evolution to be dismissed as “impossible” - - if, in fact, God chooses to use Evolution as one of his tools of creation!
