In the Lord's Prayer, do some Churches Omit "Thine is the Kingdom and the Power and the Glory," as a later addition?
For Roman Catholics the traditional Mass omits the phrasing. In the Mass of Pope Paul VI the phrase is equally not said as immediately part of the Our Father.
The liturgy of the Mass, known as the Tridentine Mass does not have the extended phrase ”For thine is the kingdom and the power and the glory, for ever. Amen.” The Order of the Mass (The Extraordinary Form of the Roman Rite)
In the Mass of Pope Paul VI the extended doxology is not said at Mass. See: The Order of Mass The extended part is in the New Mass, but a prayer (Deliver us, Lord, we pray, from every evil,
graciously grant peace in our days,
that, by the help of your mercy,
we may be always free from sin
and safe from all distress,
as we await the blessed hope
and the coming of our Saviour, Jesus Christ) comes between the two thus not making it part of the Our Father properly speaking.
The Catechism of the Catholic Church has the following to say about the Our Father:
II. The Lord's Prayer
2765 The traditional expression "the Lord's Prayer" - oratio Dominica - means that the prayer to our Father is taught and given to us by the Lord Jesus. the prayer that comes to us from Jesus is truly unique: it is "of the Lord." On the one hand, in the words of this prayer the only Son gives us the words the Father gave him:13 he is the master of our prayer. On the other, as Word incarnate, he knows in his human heart the needs of his human brothers and sisters and reveals them to us: he is the model of our prayer.
2766 But Jesus does not give us a formula to repeat mechanically.14 As in every vocal prayer, it is through the Word of God that the Holy Spirit teaches the children of God to pray to their Father. Jesus not only gives us the words of our filial prayer; at the same time he gives us the Spirit by whom these words become in us "spirit and life."15 Even more, the proof and possibility of our filial prayer is that the Father "sent the Spirit of his Son into our hearts, crying, 'Abba! Father!'"16 Since our prayer sets forth our desires before God, it is again the Father, "he who searches the hearts of men," who "knows what is the mind of the Spirit, because the Spirit intercedes for the saints according to the will of God."17 The prayer to Our Father is inserted into the mysterious mission of the Son and of the Spirit.
The extended phrase is said at New Mass but not part of the Our Father. Also Catholic may say the extended version as their own form of piety, but it is not an obligation.