What’s a Liturgy?
The word leitourgia is a technical term in ancient Greek signifying a public work at private expense. In the Septuagint it (and the verb leitourgeo) is used for the public service of the temple (e.g., Exodus 38:27; 39:12, etc.). Thence it comes to have a religious sense as the function of the priests, the ritual service of the temple (e.g., Joel 1:9, 2:17, etc.). In the New Testament this religious meaning has become definitely established. In Luke 1:23, Zachary goes home when "the days of his liturgy" (ai hemerai tes leitourgias autou) are over. In Hebrews 8:6, the high priest of the New Law "has obtained a better liturgy", that is a better kind of public religious service than that of the Temple.
So in Christian use liturgy meant the public official service of the Church, that corresponded to the official service of the Temple in the Old Law. It is sometimes referred to as “the work of the people” but it should more properly be considered the work of God as He gathers and feeds His people.
God gathers us together in the name of the Father and the Son and the Holy Spirit, the name into which we were baptized. He gathers us to receive His gifts—Himself, His name, His flesh and blood Son, His Word of pardon and peace, His life, His grace and Spirit. In the Divine Service He distributes these gifts to us. Here we receive the forgiveness of sins, life, and salvation Christ won for us on the cross. God calls and gathers us into His holy Christian church where we have communion with Him and all His saints in heaven and on earth. Heaven and earth intersect in the Divine Service.
(Lutheran Church–Canada Committee on Worship and Music)
The Service of the Word has its roots in ancient Judaic synagogue Sabbath worship. First are some introductory prayers, then a call to worship and the “Shema” and the Blessings, then a prayer called the “Amidah” (aka “Shemona Esrei”) and on Sabbath readings from Jewish Bible (the Old Testament) with some explanation, and then concluding prayers. The liturgy follows the same pattern with adaptations to reflect Christ's incarnation, death, and resurrection as the Jewish Messiah.
The second part is the Service of the Sacrament or the Lord's Supper.
The Lord's Supper is patterned after the Jewish "Seder Service", the last meal shared by Jesus and His disciples. At the seder meal Jesus changed the age-old blessings over the bread and the fruit of the vine, saying "Take and eat, this is my body" over the bread and "Take and drink, this is my blood" over the fruit of the vine. Unmistakeable if you are familiar with a seder meal; Jesus was making himself the Passover lamb and serving Himself to them.
Thus the pastor repeats the “Words of Institution" during the Service of the Lord’s Supper,
“Our Lord Jesus Christ, on the night when he was betrayed, took the bread, and when he had given thanks, he broke it and gave it to his disciples and said, 'Take; eat; this is my body which is given for you. This do in remembrance of me.' In the same way he also took the cup after the supper, and when he had given thanks, he gave it to them saying, 'Drink of it, all of you. This cup is the New Testament in my blood, shed for you for the forgiveness of sins. This do, as often as you drink it, in remembrance of me.'
“Liturgy”, or "Divine Service", then, is the service of God to us, first of His Word and then the Sacrament of his Body and Blood. A Christian “Sabbath service” followed by a Christian “Seder meal”. As far back as can be determined the church has followed a similar pattern of worship, a pattern of worship whose roots are deeply set in the traditions of the ancient Judaism from whence our faith and our Saviour was delivered to us. In a time when so many worshippers hope to restore an “uncorrupted”, “simple”, and “early” Christian worship style it is passing strange that so few understand the meaning and history of the liturgical service. The liturgy is the “uncorrupted”, “simple”, and “early” Christian worship style. The buildings might be a little more elaborate, as are the priestly vestments, but the service is virtually the same as that practiced by the Apostles.
“The core of liturgics is not just beautiful music or awe-inspiring ritual, rather it is a commitment to origins. Two concepts need to be kept in mind as one considers the "why" of liturgical worship and practice: origin and changelessness. Remember, first and foremost, that the Apostles and the first Christian disciples were Jews. That is, they were Jews who recognized and accepted Jesus Christ as the promised Messiah. From their heritage with its history of liturgical interaction with God, came the Jewish form of biblical worship, the basic structure, the "origin" of Christian worship. For this reason, we see in Church history a highly developed Christian liturgical order in use even by the end of the first century — that is, within sixty years of Christ’s resurrection.”
Liturgica.com
Grace Lutheran Church, Tulsa, Oklahoma. Looking at the Liturgy of the Lutheran Church.