Based on the inherent properties of water molecules, what effect would a large body of water have on the temperature of a climate?

A large body of water would stabilize the temperature of a climate.
Water has a high specific heat capacity, which means that it takes a lot of energy to heat it up or cool it down. This means that large bodies of water can act as heat sinks, absorbing heat from the surrounding air in the summer and releasing it in the winter.
This helps to moderate the temperature of the surrounding climate, making it less extreme. For example, coastal regions tend to have milder winters and cooler summers than inland regions.