Why is the heliocentric theory so important?

The theory is important because Nicolas Copernicus claimed that the sun was in the middle of the galaxy and we revolved around the sun.

The heliocentric theory is so important because it's the theory which is still known to be correct today (and eventually gave rise to the development of science). The reason for this is that the previous geocentric model which said that the Earth was in middle of the Universe was flat out wrong and only supported by the Church but not by evidence.