Do you accept everything that Eusebius wrote as accurate and representative of the church of his day? What about his comments on Christ’s attonement for our sins, which looks very much like penal substitution and what he3 has to say about the Eucharist involving symbols?
And the Lamb of God not only did this, but was chastised on our behalf, and suffered a penalty He did not owe, but which we owed because of the multitude of our sins; and so He became the cause of the forgiveness of our sins, because He received death for us, and transferred to Himself the scourging, the insults, and the dishonour, which were due to us, and drew down on Himself the apportioned curse, being made a curse for us.
(Demonstratio Envangelica, Book 10, Chapter 1)
He then that was alone of those who ever existed, the Word of God, before all worlds, and High Priest of every creature that has mind and reason, separated One of like passions with us, as a sheep or lamb from the human flock, branded on Him all our sins, and fastened on Him as well the curse that was adjudged by Moses’ law, as Moses foretells: “Cursed is every one that hangeth on a tree.” This He suffered "being made a curse for us; and making himself sin for our sakes."And then "He made him sin for our sakes who knew no sin,"and laid on Him all the punishments due to us for our sins, bonds, insults, contumelies, scourging, and shameful blows, and the crowning trophy of the Cross. And after all this when He had offered such a wondrous offering and choice victim to the Father, and sacrificed for the salvation of us all, He delivered a memorial to us to offer to God continually instead of a sacrifice.
(Demonstratio Envangelica, Book 1, Chapter 10)
]He gave Himself the symbols of His divine dispensation to His disciples, when He bade them make the likeness of His own Body. For since He no more was to take pleasure in bloody sacrifices, or those ordained by Moses in the slaughter of animals of various kinds, **and was to give them bread to use as the symbol of His Body, **He taught the purity and brightness of such food by saying, “And his teeth are white as milk.” This also another prophet has recorded, where he says, “Sacrifice and offering hast thou not required, but a body hast thou prepared for me.”
(Demonstratio Envangelica, Book 8, 380b)
And he adds: “I have preached righteousness in the great congregation.” He plainly teaches that in place of the ancient sacrifices and whole burnt-offerings the incarnate presence of Christ that was prepared was offered. And this very thing He proclaims to his Church as a great mystery expressed with prophetic voice in the volume of the book. As we have received a memorial of this offering which we celebrate on a table by means of symbols of His Body and saving Blood according to the laws of the new covenant, we are taught again by the prophet David to say:
“5. Thou hast prepared a table before me in the face of my persecutors. Thou hast anointed my head with oil, and thy cup cheers me as the strongest (wine).”
(Demonstratio Envangelica, Book 1, 37b)
Then too, Eusebius was apparently sympathetic to Arianism. Does this place him squarely in the Catholic Church?
Alexander, Bishop of Alexandria, excommunicated Arius about the year 320. The Arians soon found that for all practical purposes Eusebius was on their side. He wrote to Alexander charging him with misrepresenting the teaching of the Arians and so giving them cause "to attack and misrepresent whatever they please…After some delay Eusebius subscribed to the uncompromising creed drawn up by the council, making no secret, in the letter which he wrote to his own Church, of the non-natural sense in which he accepted it. Between 325 and 330 a heated controversy took place between Eusebius and Eustathius, Bishop of Antioch. Eustathius accused Eusebius of tampering with the faith of Nicæa; the latter retorted with the charge of Sabellianism. In 331 Eusebius was among the bishops who, at a synod held in Antioch, deposed Eustathius. He was offered and refused the vacant see. In 334 and 335 he took part in the campaign against St. Athanasius at the synods held in Cæsarea and Tyre respectively. From Tyre the assembly of bishops were summoned to Jerusalem by Constantine, to assist at the dedication of the basilica he had erected on the site of Calvary. After the dedication they restored Arius and his followers to communion.