Diversity is all about reception and freedom from dropouts, and most wireless brands tout it as a selling feature. One external sign of diversity is the presence of two antennas on the receiver, although not all dual-antenna receivers have true diversity. Receivers with true diversity circuitry have two separate radio receiver modules, each connected to its own antenna. The signals from the two antennas are monitored and the one receiving the stronger signal is automatically selected. Reception is in part a function of position, and is influenced by the relative locations of the transmitter and receiver. By having two antennas, you reduce the chance of dropouts occurring.
If your system is intended for use in a single location, and especially an open location such as a house of worship, you likely won’t gain much by having a true-diversity receiver. However, if you will use the system in various locations that may have structures that block or deflect wireless transmissions, diversity is more important.