Ignatius of Antioch

Being mindful of your love and of your zeal in Christ, which ye have manifested towards us, we thought it fitting to write to you, who display such a godly and spiritual love to the brethren, to put you in remembrance of your Christian course, "that ye all speak the same thing, being of one mind, thinking the same thing, and walking by the same rule of faith," as Paul admonished you. For if there is one God of the universe, the Father of Christ, "of whom are all things; " and one Lord Jesus Christ, our [Lord], "by whom are all things; " and also one Holy Spirit, who wrought in Moses, and in the prophets and apostles; and also one baptism, which is administered that we should have fellowship with the death of the Lord; and also one elect Church; there ought likewise to be but one faith in respect to Christ. For "there is one Lord, one faith, one baptism; one God and Father of all, who is through all, and in all."

There is then one God and Father, and not two or three; One who is; and there is no other besides Him, the only true [God]. For "the Lord thy God," saith [the Scripture], "is one Lord." And again, "Hath not one God created us? Have we not all one Father? And there is also one Son, God the Word. For "the only-begotten Son," saith [the Scripture], "who is in the bosom of the Father." And again, "One Lord Jesus Christ." And in another place, "What is His name, or what His Son's name, that we may know? " And there is also one Paraclete. For "there is also," saith [the Scripture], "one Spirit," since "we have been called in one hope of our calling." And again, "We have drunk of one Spirit," with what follows. And it is manifest that all these gifts [possessed by believers] "worketh one and the self-same Spirit." There are not then either three Fathers, or three Sons, or three Paracletes, but one Father, and one Son, and one Paraclete. Wherefore also the Lord, when He sent forth the apostles to make disciples of all nations, commanded them to "baptize in the name of the Father, and of the Son, and of the Holy Ghost," not unto one [person] having three names, nor into three [persons] who became incarnate, but into three possessed of equal honour.