Psalms 19:15

יִהְיוּ לְרָצוֹן אִמְרֵי פִי וְהֶגְיוֹן לִבִּי לְפָנֶיךָ ה’ צוּרִי וְגֹאֲלִי

May the words of my mouth and the meditation of my heart be acceptable before You, Hashem, my rock and my redeemer.

This verse, recited at the end of Shemoneh Esrei, is a prayer for the acceptance of what had been said previously. The Talmud (Brachos 9b) explains that it was placed here because David said it at the conclusion of the 19th Psalm. It is therefore fitting to recite it at the conclusion of our 19 brachos.