What made Shylock say, ‘A Daniel is come to judgement!’?
This is a Biblical allusion referring to the story of Daniel and the Lion's Den. Basically, Daniel was an wronged innocent who was thrown into the lion's den to be devoured. However, because of his innocence, he was protected from the lions and was able to walk unharmed from the den the next day...much to the shock and dismay of those who caused him to be punished in such a way.
In this play, Shylock, a Jewish money-changer (and known for his greed and ruthless business acumen) is using this allusion to suggest that Antonio (who has agreed to borrow money from Shylock on credit to help a friend) is the innocent who has been wronged by Bassanio since the loan has come due and the money isn't available to Antonio to pay it back. The allusion works since Antonio (the symbolic Daniel) has been duped and thrown into the lion's pit--the money borrowing business--but things have not worked out so well for him as they did for the Biblical Daniel. Shylock's Jewish ancestry also makes the allusion that much more effective since he would know the Bible's contents well, thus he is able to make such comparisons relatively easily.