In Defense of the Conclusion

Westminster Larger Catechism #196:

Q. What doth the conclusion of the Lord's prayer teach us?
A. The conclusion of the Lord's prayer (which is, For thine is the kingdom, and the power, and the glory, forever. Amen.) teacheth us to enforce our petitions with arguments, which are to be taken, not from any worthiness in ourselves, or in any other creature, but from God; and with our prayers to join praises, ascribing to God alone eternal sovereignty, omnipotency, and glorious excellency; in regard whereof, as he is able and willing to help us, so we by faith are emboldened to plead with him that he would, and quietly to rely upon him, that he will fulfill our requests. And, to testify this our desire and assurance, we say, Amen.