7 has had significance in almost every major religion. In the Old Testament the world was created in six days and God rested on the seventh, creating the basis of the seven-day-week we use to this day. In the New Testament the number seven symbolizes the unity of the four corners of the Earth with the Holy Trinity.
1977 the year of Close Encounters!
Steven Spielberg had much "special" in put to the making of this film.