Reading this, you must understand that the wedding garment is the robe of righteousness given to us by Christ. It's His own righteousness given to us. I think it's interesting there is a man who is in the wedding hall who got in, but apparently tried doing it by another way. Which of course reminds me of what Jesus said in the beginning of John chapter 10: "Truly, truly, I say to you, he who does not enter the sheepfold by the Door but climbs in by another way, that man is a thief and a robber."
The man did not come with the robe of righteousness. He obviously tried to get in, but not according to the rules. He tried to sneak in without the righteousness of Jesus Christ. He tried to sneak in with his own righteousness and his own clothes and not the proper wedding garment. And so Jesus says, "How did you get in here?" And the guy was speechless. He had nothing to say for himself. There was nothing he could boast about when he saw the King Himself. He realized the futility of trying to get in his own way and how pitiful a plan it was.
There apparently will be people on judgment day who will stand before the King in their own rags, speechless, without a single thing to say. It will be plain to them then that, "through obedience to the law, no man shall be justified."