Nations around the Israelites had many gods that they worshipped. One of those countries was Egypt. They were very familiar with idol worship while they were there, but God made it very plain that He was number one. There was to be no idol worship among them.
God has always been very specific about the way He wants people to worship Him. He gave Moses instructions for the type of altar that He required His people to use in their worship. It was to be built out of earth or they could choose uncut stone. At that time, He wasn’t interested in fancy structures of worship. Splendor would be expected later.