The verse stems from the parable of the wedding banquet in Mathew 22. In After a king invited many guests for his son's wedding, those invited made excuses and didn't come, others killed the servents of the king. so the king sent an army to deal with those who were murders and sent his servents to the street corners and invited everyone they could to the banquet. To fill the banquet.
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From this, the parable makes sense and I've thought about it being an explanation that Isreal rejected Jesus, so God send out for everyone to be invited and brings the salvation to Gentiles and all nations. However the parable continues, and I too have trouble understanding it.
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Then the king went out to see the guests, and found a man not wearing wedding clothes. He said "how did you get in without wedding clothes?" The man was speechless, so the king ordered his servents to bind up the man and throw him out. And that's then where the verse in Mathew 22:14 say "many are called but few are chosen."
I don't know the meaning of it or the meaning of the wedding clothes. But in a bible study I was in, someone explained that there is context regarding the wedding clothes. It might have been easily understood when Jesus gave this parable. As it was explained to me when people are invited to a king's wedding, they are also given something to wear for the occasion. In that bible study it was compaired to the teaching that those saved will be given white clothes washed by the blood of the Lamb of God. If this is true (I have no idea how to find out if the context of the king providing clothes is right), if it's true then this is an awesome aspect and hope for those of us who are Christian and have faith in Jesus for our hope and our salvation.
But then comes verse 14. "Many are called but few are chosen." And the interloper who sneaked into the banquet without the wedding clothes. I honestly don't know how to understand the parable except in parts. Trying to look at it in it's whole context, I have to question if any Christian might be like the man without wedding clothes. Some how missing the mark. Called but not chosen.