He then again admirably discusses the term πρωτότοκος as it is four times employed by the Apostle
But that the readers of our work may find no ambiguity left of such a kind as to afford any support to the heretical doctrines, it may be worth while to add to the passages examined by us this point also from Holy Scripture. They will perhaps raise a question from the very apostolic writings which we quoted: “How could He be called 'the first-born of creation ' if He were not what creation is? For every first-born is the first-born not of another kind, but of its own: as Reuben, having precedence in respect of birth of those who are counted after him, was the first-born, a man the first-born of men; and many others are called the first-born of the brothers who are reckoned with them.” They say then, “We assert that He Who is 'the first-born of creation' is of that same essence which we consider the essence of all creation. Now if the whole creation is of one essence with the Father of all, we will not deny that the first-born of creation is this also: but if the God of all differs in essence from the creation, we must of necessity say that neither has the first-born of creation community in essence with God.” The structure of this objection is not, I think, at all less imposing in the form in which it is alleged by us, than in the form in which it would probably be brought against us by our adversaries. But what we ought to know as regards this point shall now, so far as we are able, be plainly set forth in our discourse.
Four times the name of “first-born” or “first-begotten” is used by the Apostle in all his writings: but he has made mention of the name in different senses and not in the same manner. For now he speaks of “the first-born of all creation,” and again of “the first-born among many brethren,” then of “the first-born from the dead;” and in the Epistle to the Hebrews the name of “first-begotten” is absolute, being mentioned by itself: for he speaks thus, “When again He brings the first-begotten into the world, He says, 'Let all the angels worship Him. '” As these passages are thus distinct, it may be well to interpret each of them separately by itself, how He is the “first-born of creation,” how “among many brethren,” how “from the dead,” and how, spoken of by Himself apart from each of these, when He is again brought into the world, He is worshipped by all His angels. Let us begin then, if you will, our survey of the passages before us with the last-mentioned.
“When again He brings in,” he says, “the first-begotten into the world.” The addition of “again” shows, by the force of this word, that this event happens not for the first time: for we use this word of the repetition of things which have once happened. He signifies, therefore, by the phrase, the dread appearing of the Judge at the end of the ages, when He is seen no more in the form of a servant, but seated in glory upon the throne of His kingdom, and worshipped by all the angels that are around Him. Therefore He Who once entered into the world, becoming the first-born “from the dead,” and “of His brethren,” and “of all creation,” does not, when He comes again into the world as He that judges the world in righteousness, as the prophecy says, cast off the name of the first-begotten, which He once received for our sakes; but as at the name of Jesus, which is above every name, every knee bows, so also the company of all the angels worships Him Who comes in the name of the First-begotten, in their rejoicing over the restoration of men, wherewith, by becoming the first-born among us, He restored us again to the grace which we had at the beginning. For since there is joy among the angels over those who are rescued from sin, (because until now that creation groans and travails in pain at the vanity that affects us, judging our perdition to be their own loss,) when that manifestation of the sons of God takes place which they look for and expect, and when the sheep is brought safe to the hundred above, (and we surely— humanity that is to say— are that sheep which the Good Shepherd saved by becoming the first-begotten,) then especially will they offer, in their intense thanksgiving on our behalf, their worship to God, Who by being first-begotten restored him that had wandered from his Father's home.
Source: Against Eunomius (New Advent)