Shawn Holes admitted breaching the peace earlier this month by "uttering homophobic remarks" that were "aggravated by religious prejudice".
The American Baptist, who was touring Britain with colleagues, was arrested by police while responding to questions from people in Sauchiehall Street on 18 March.
Holes, 47, from New York State, when asked his views on gay people, said: "Homosexuals are deserving of the wrath of God – and so are all other sinners – and they are going to a place called hell."
He said later: "There were homosexuals listening – around six or eight of them – who were kissing each other and cuddling, and asking 'What do you think of this?'
"It felt like a set-up by gay campaigners. When asked directly about homosexuality, I told them homosexuals risked the wrath of God unless they accepted Christ."
Holes said he had no choice but to admit the charge at Glasgow Sheriff Court because he was desperate to fly home to see his wife, and his father, who is in a hospice. However, he said he had expected to be fined only about 100.
New legislation introduced last week increased the penalties available for people convicted of "hate crimes" against groups such as gay and disabled people to the same level as race crimes.
But Tony Kelly, Holes' lawyer, said: "This case raises important issues about the interface between the criminal law and religious freedom."
Gordon Macdonald, of Christian Action Research and Education for Scotland, said: "This is a concerning case. I will be writing to Chief Constable Stephen House of Strathclyde Police for clarification of the guidance given to police officers in these situations."
The Roman Catholic Church, which backed stiffer "hate crime" penalties, said the fine seemed to criminalise anyone who repeated a widely held conviction.
Peter Kearney, its spokesman, said: "We supported this legislation but it is very difficult to see how this man can be charged for expressing a religious conviction.
"The facts of this case show his statement was clearly his religious belief.
"Yes, it is strong language he has used, but it is obviously a religious conviction and not a form of discrimination."