Ante-Nicene Fathers, Vol IX:
Origen's Commentary on the Gospel of Matthew.: Chapter IV

4.  Harmony of the Old and New Covenants.

And likewise it is a pleasant thing to endeavour to understand and exhibit the fact of the concord of the two covenants,—of the one before the bodily advent of the Saviour and of the new covenant; for among those things in which the two covenants are at concord so that there is no discord between them would be found prayers, to the effect that about anything whatever they shall ask it shall be done to them from the Father in heaven.  And if also you desire the third that unites the two, do not hesitate to say that it is the Holy Spirit, since “the words of the wise,” whether they be of those before the advent, or at the time of the advent, or after it, “are as goads, and as nails firmly fixed, which were given by agreement from one shepherd.” 6069   And do not let this also pass unobserved, that He did not say, where two or three are gathered together in My name, there “shall I be” in the midst of them, but “there am I,” 6070 not going to be, not delaying, but at the very moment of the concord being Himself found, and being in the midst of them.

Footnotes

Eccl. xii. 11.

Matt. xviii. 20.