Some scholars contend that the precedent for the “Lord’s Prayer” (St. Matt. 6:9-13; St. Luke 11:2-4) was set by the second-temple Judæan קדיש (“Qaddish” - Aramaic for “holy” or “sanctification”), which was an invocation made at the end of synagogue services (the precursor to the Christian “liturgy of the word”). Per Deiss: “The first two petitions inspired the first two petitions of the Lord’s Prayer” (Springtime of the Liturgy, p. 17). The petitions, which speak to the sanctification of the name of the Lord (viz. “hallowed be thy name”), are as follows:
May his great name be magnified and sanctified in the world that he created according to his good pleasure. May he make his reign prevail during your life and during your days, and during the life of the entire house of Israel, at this very moment and very soon. And let them say: Amen!
May the name of the Lord — blessed be he! — be blessed, praised, glorified, extolled, exalted, honored, magnified, and hymned! It is above and beyond any blessing, hymn, praise, consolation that men utter in this world. And let them say: Amen!
The eschatological (and even apocalyptic) phrasing of “thy kingdom come, thy will be done, on earth as it is in heaven” in the Lord’s Prayer mirrors that of “may he make his reign [synonymous with the idea of "kingdom" here] prevail during your life … and during the life of the entire house of Israel.”
However, the most significant departure from the Judæan קדיש is our Lord’s usage of the word “Abba” to address God the Father. Deiss notes that “Abba was a child’s word, used in everyday talk … He spoke to God as a child to its father, confidently and securely, and yet at the same time reverently and obediently” (Ibid. p. 18). By commanding his followers to pray to the Father in the same manner — as Abba – the scandal is repeated throughout history. This is why, in the Divine Liturgy, the priest says aloud: “And make us worthy, O Master, that with boldness and without condemnation, we may dare to call upon Thee, the Heavenly God as Father and to say: ‘Our Father, who art in heaven …’”
We dare to call upon the Father as “Abba” because Christ himself dared to do so, and because he taught his disciples to do the same. He secured our intimacy with the Father through himself, making his Father to be our own and restoring the communion that was lost in the Garden. Christ is the Son of God by nature, begotten and not made, and we are sons of God — Christians or “little Christs” — by grace, being transformed into his likeness. And it is in his likeness, by virtue of our union with him, that we dare to call upon our Heavenly God as Father and to say: “Abba.”