Originally, in biblical times, Pentecost was primarily a harvest festival, but after the time of Jesus and the fall of Jerusalem to the Romans it became more focused on the fact that according to Exodus 19:1, fifty days after Israel came out of Egypt, God brought them to Sinai to establish His covenant with them and to give them His Law through His Prophet Moses. So from the institution of the feast of Passover, which led to the liberation of the Jews from bondage in Egypt, until God brought them to Mount Sinai to deliver His law to His people, fifty days passed. By being given a law and having God as their Ruler, they would be able to enter the Promised Land as one nation.
In the Orthodox Church, on the feast of Easter, which is known as Pascha (the Greek word for Passover), we celebrate the liberation of the human race from the bondage of sin, death and the devil through the crucifixion and resurrection of Jesus Christ, and over a period of fifty days until the feast of Pentecost we are led on a journey to receive from God His Holy Spirit, through whom the law of God is written in our hearts instead of on tablets of stone. When the law of God is written in our hearts through the Holy Spirit, we become united citizens of God's eternal kingdom. The fifty day period between Easter and Pentecost is known in the Orthodox Church as the Pentecostarion.
In the Orthodox Church, on the feast of Easter, which is known as Pascha (the Greek word for Passover), we celebrate the liberation of the human race from the bondage of sin, death and the devil through the crucifixion and resurrection of Jesus Christ, and over a period of fifty days until the feast of Pentecost we are led on a journey to receive from God His Holy Spirit, through whom the law of God is written in our hearts instead of on tablets of stone. When the law of God is written in our hearts through the Holy Spirit, we become united citizens of God's eternal kingdom. The fifty day period between Easter and Pentecost is known in the Orthodox Church as the Pentecostarion.