To answer this question we first need to know something about where we get the Lord's Prayer, in it's various forms as prayed by Catholics and Protestants.
What you are referring to as "finishing" the Lord's Prayer is actually a doxology (a prayer of praise) added to the prayer which Jesus taught to his disciples (as recorded in the scriptures.)
The Lord's Prayer is recorded in only two of the Gospels (Mt 6 and Lk 11), and in neither of these versions is the final doxology ("for thine is the kingdom...) included. In fact, the final doxology is actually a combination of several prayers of praise recorded in various parts of the Book of Revelation.
Early on in the life of the Church (within the first century) Christians began concluding the Lord's Prayer with this doxology when they prayed at their liturgies. (An example of this is recorded in the Didache.)
Today, in our Catholic Mass, we retain the version of the Lord's Prayer as it is recorded in Matthew's Gospel. This version divides the Lord's Prayer into seven petitions for which we pray to the Father. The final doxology is separated by a short insertion ("Deliver us, Lord...) which indicates that this prayer of praise (the final doxology) glorifies God for the fulfillment of the first three petitions (hallowed be thy name... thy kingdom come... thy will be done...), which has occurred, but is not yet fully experienced by us on earth ("as we await the coming of our savior..."). |
