Their decisions made up the common law. In a jury trial, the jury is selected by the parties through a process called voir dire, where the judge or parties ask jurors questions in order to determine their biases and opinions. After the jury is chosen and sworn in, the parties give opening arguments, present their evidence and give closing arguments. The role of the jury is to decide issues of fact. Parties are entitled to a jury trial by the federal constitution in those types of cases, such as breach of contract, which existed in 1789, the effective date of the constitution.
States are free to make jury trials available for such actions, but few have.
In fact, only Texas and Georgia permit jury trials for divorces.