If Yahshua had been teaching "directly," as in the Olivet discourse, He might have used a more descriptive or technical term, but because this is a parable, the ordinary word for "garment" would naturally have been used. Yahshua left it up to us to make the connection between the symbol and the reality it represents. His parables always follow this pattern. It's pretty obvious that you're right, Yada: the wedding garment surely represents the "garment of light" of which Yada speaks, described elsewhere as "fine linen, clean and bright (lampros = radiant), for the fine linen is the righteous acts of the saints" (Rev 19:8), which as we know can only mean imputed righteousness, the righteousness of our Messiah, for our own "righteous acts" aren't worth all that much.

So there are a couple of things to note concerning the parable: (1) The garment was freely available to all the wedding guests; all the guy had to do was put it on. (2) Because of this, his presense at the party without it was a mark of utter disrespect for the "sovereign" who had paid for the garment. (3) The guy had come into the party and made himself at home without wearing the garment---nobody confronted him until the king did, because nobody else had the authority to do so (see Rev. 5:4-5). (4) The guy was "speechless" because there was absolutely no excuse for not accepting the free gift and donning the garment of light. And (5) The eviction of the offender was based not on his lack of an invitation to the party, but on his lack of reverence and respect for the King.

kp