The reading is from St. Paul's Letter to the Galatians 3:15-22

Brethren, to give a human example: no one annuls even a man's covenant, or adds to it, once it has been ratified. Now the promises were made to Abraham and to his offspring. It does not say, "And to your offsprings," referring to many; but, referring to one, "And to your offspring," which is Christ. This is what I mean: the law, which came four hundred and thirty years afterward, does not annul a covenant previously ratified by God, so as to make the promise void. For if the inheritance is by the law, it is no longer by promise; but God gave it to Abraham by a promise. Why then the law? It was added because of transgressions, till the offspring should come to whom the promise had been made; and it was ordained by angels through an intermediary. Now an intermediary implies more than one; but God is one. Is the law then against the promises of God? Certainly not; for if a law had been given which could make alive, then righteousness would indeed be by the law. But the scripture consigned all things to sin, that what was promised to faith in Jesus Christ might be given to those who believe.