No language in the history of the world has lasted thousands of years without changes along the way. Egyptian language has gone through 6 stages to get to where we are today.
Since 3000 BC, Egyptian writing has been in a form of pictures, signs, and labels. Old Egyptian was created in 2600BC and was used as the national language for over 500 years. Middle Egyptian then took over as the mainstream language as of 2100BC and survived unchanged for another 500 years until Late Egyptian took its place. Egyptian demotic language derived around 650BC and survived until 5AD. Coptic is a Bohraic dialect and now seen as a religious or holy language. This old form of communication is commonly used in Egyptian Christian Churches. Demotic survived as a written, living language until 2AD.
Old, Middle, and Late Egyptian were in the forms of hieroglyphs. Demotic language looks very similar to Arabic, but the two are not related in anyway. Coptic uses the Greek alphabet but also a number of symbols were added for sounds that were not in the Greek language. Arabic became the official language after Egypt was invaded by Arabia in the 17th century.
Ancient Egyptian language is a combination of Arabic, Hebrew, and African tribal languages. Its word-stems are made up of combinations of consonant letters. Through its more than 3.000 year long history, it is but natural that the language of the Ancient Egyptians changed and evolved both grammatically and semantically. Considering grammatical evolution, several linguistic stages, more or less coinciding with important stages in history can be distinguished. The language was divided into categories that describe the period in history from which they came.
Old Egyptian is the language of the Early Dynastic Period and Old Kingdom. The earliest surviving texts from this language dates back to 3200 BC. Most texts of this period are official or religious, with funerary inscriptions and some biographical texts.
Middle Egyptian is a more evolved form of Old Egyptian. This language became the classical language of the Egyptian texts, which include religious inscriptions, medical and scientific texts as well as literature and wisdom texts.
Late Egyptian (or New Egyptian) was the vernacular used from the 18th Dynasty on, which found its way in writing, mainly in business documents and letters. The fact that it was used by merchants and common businessmen of the time leads historians and archaeologists to believe that it was a more commonly spoken language than Old and Middle Egyptian.
Coptic is a transitionary type language written in Greek alphabet. Initially it was spoken by Egyptian Christians, but became widely used as Greek influence spread. Its vocabulary is also highly influenced by Greek language. Arabic would eventually replace this as the written and spoken language of Egypt beginning with the Arab conquest of Egypt in 640 A.D. Currently, Coptic is important and liturgical (meaning used in religious services) to Egyptians much like Latin is important to Europeans. Also, much of the old transcripts and parchment of the Ancient times exist in a Coptic form.