St. Ignatius to the Magnellians 9-10:
If, therefore, those who were brought up in the ancient order of things have come to the possession of a new hope, no longer observing the Sabbath, but living in the observance of the Lord's Day, on which also our life has sprung up again by Him and by His death— whom some deny, by which mystery we have obtained faith, and therefore endure, that we may be found the disciples of Jesus Christ, our only Master— how shall we be able to live apart from Him, whose disciples the prophets themselves in the Spirit did wait for Him as their Teacher? And therefore He whom they rightly waited for, having come, raised them from the dead.
Let us not, therefore, be insensible to His kindness. For were He to reward us according to our works, we should cease to be. Therefore, having become His disciples, let us learn to live according to the principles of Christianity. For whosoever is called by any other name besides this, is not of God. Lay aside, therefore, the evil, the old, the sour leaven, and be changed into the new leaven, which is Jesus Christ. Be salted in Him, lest any one among you should be corrupted, since by your savour you shall be convicted. It is absurd to profess Christ Jesus, and to Judaize. For Christianity did not embrace Judaism, but Judaism Christianity, that so every tongue which believes might be gathered together to God.