Question: "Should "for thine is the kingdom, and the power, and the glory, forever" be included in the Lord's Prayer (Matthew 6:13)?"
Answer: Matthew 6:9–13 includes what is commonly referred to as The Lord’s Prayer, because in this section Jesus teaches His disciples how they should pray (Matthew 6:9). But the careful reader will notice that the ending is different in different translations, inviting the question as to whether “for thine is the kingdom, and the power, and the glory, forever” should be included in the Lord’s Prayer. The King James Version contains the ending, while the English Standard Version (ESV) and New International Version (NIV), do not. The New American Standard Bible (NASB) includes the statement in brackets with an editorial note that the oldest manuscript does not include the words.
Should “for thine is the kingdom, and the power, and the glory, forever” be included in the Lord’s Prayer (Matthew 6:13)? Luke might suggest not, as his gospel includes a slightly abbreviated account of the prayer (Luke 11:2–4) and excludes the “kingdom . . . power . . . glory” statement. Of course, Luke’s account does not provide evidence of what Matthew wrote, but it does show at least what Luke felt was germane to reproduce.
The phrase “for thine is the kingdom, and the power, and the glory, forever,” as part of the Lord’s Prayer (Matthew 6:13), is absent from the early Greek manuscripts like Sinaiticus (א) and Vaticanus (B), both 4th-century manuscripts; Bezae (D) from the 5th century; and Dublinensis (Z) from the 6th century. The absence of the phrase in these early Greek manuscripts is a significant evidence that the words were not original in Matthew’s Gospel. That it is absent in the writings of early theologians like Tertullian (2nd—3rd centuries), Origen (3rd century), Cyprian (3rd century), Ambrose (4th century), and Augustine (4th—5th centuries) also suggests that “for thine is the kingdom, and the power, and the glory, forever” was not originally included in the Lord’s Prayer.
On the other hand, there are some early references to the phrase, including in the very early (2nd-century) Didache [minus he basileia (“the kingdom”)] (Kirsopp Lake, The Apostolic Fathers, Volume I, G.P. Putnam’s Sons, 1919, p. 320). While the phrase is absent from the earliest Greek Bible manuscripts, it is present in the majority of later Greek manuscripts and an increasing number of theological writings as time went on.
The question of whether or not “for thine is the kingdom, and the power, and the glory, forever” was included in the Lord’s Prayer is not easily answered, as there is data to support both perspectives. The earliest evidence of the Greek Bible manuscripts supports the exclusion of the phrase, while its widespread presence in later manuscripts means the phrase cannot be discarded lightly. Based on these data points, it would seem that the addendum to Matthew 6:13 may have been an editorial doxological addition first in the Didache (an extrabiblical document) and slightly refined to include the kingdom as time progressed.
The doxology “for thine is the kingdom, and the power, and the glory, forever” seems most likely to be a kind of hymnic addition to facilitate a worshipful reading of the passage. While the statement is certainly true—God’s is the kingdom, the power, and the glory forever—it was probably not originally in Matthew’s Gospel (particularly if one weighs heavily the earliest Greek manuscripts, as does the NASB, for example).