Why was being a tomb builder considered a very important job in ancient egypt?

The tomb builder's position in Egypt was very important because tombs were built for the highest persons in the land, the pharaohs, both as a monument to their greatness and to aid them in the afterlife.

The pharaohs' tombs were enclosed in massive structures, the pyramids. The most prominent example is the Great Pyramid of Giza, built for Pharaoh Khufu (2609 BC - 2584 BC). It is the only one of the Seven Wonders of the ancient world that still stands today. It is 480 feet tall, and estimates suggest that about 20,000 workers over a period of about 20 years were needed to build the Great Pyramid. So any persons at the head of a tomb building project, for any of the pyramids, was in charge of a gigantic undertaking of engineering and coordination of efforts.