If there is a greater dew point there is more water vapor. Water vapor plays a great role in instability. If there is more water vapor there are more thunderstorms. Evaporation occurs when water changes, for every gram there is a tremendous amount of cooling. It is associated with latent heat.
Condensation does the opposite.
Moisture condenses, heat lets out in the atmosphere. Thus, if moisture is condensing in a rising air parcel that is the same temperature as the surrounding air, latent heat makes the air parcel warmer and it becomes unstable by being made warmer than the surrounding air. Thus, meteorologists often look for regions of high surface dewpoint and assume that the air there is pretty unstable. If air is unstable it will rise. If air is very humid, little lifting is needed for the air to reach saturations and for cumulonimbus clouds to develop.