Where did the idea of giving a toast begin? Was it for religious reasons?

Answer 1

I believe it has a dual origin, neither of which is religious. In the Middle Ages, there was a level of intrigue, and lots of people were assassinating one another. One of the favorite methods of the times was to invite your target over for a drink and lace his wine with poison. After a while, people caught on, but it was prohibitively impolite to refuse a drink when it was served to you. Solution: to show his goodwill, the host would pour the wine and drink first (also where the phrase 'to drink one's health' come from). The clinking of glasses may come from a continuation of this tradition. Just to be really sure your wine wasn't poisoned, a guest might actually pour some of his into the cup of his host. If he wanted to make a gesture of confidence in his host, he could just do a symbolic glass clinking.

It's called a toast because of the Romans. They actually had a custom of putting a piece of burnt toast into their cups of wine. This helped neutralize the acid and cover the bad taste of cheap wine. In some ways the Romans were like the Medievalists, and if there was a little something extra added to the wine, the burnt toast would help cover the taste of that too. This habit eventually made its way to England, and even when the practice itself died out, the phrase lived on.

Answer 2

The custom of drinking ‘health’ to the living is most probably derived from the ancient religious rite of drinking to the gods and the dead.
The Greeks and Romans at meals poured out libations to their gods, and at ceremonial banquets drank to them and to the dead.”