Eusebius's central argument is to provide a "Proof of the Gospel" by demonstrating that the coming of Christ and the establishment of Christianity were foretold in detail by the Hebrew prophets and sacred writings from the earliest times. He aims to show that these prophecies were literally fulfilled in Jesus Christ and the subsequent events, thereby validating the Christian faith to both Gentiles (who might question abandoning ancestral gods) and Jews (who might question the rejection of Mosaic law). He asserts that Christianity is not a new or original religion, but rather a re-establishment of the "most ancient" and "most venerable" form of monotheistic worship practiced by pre-Mosaic saints like Abraham, Enoch, Noah, and Job.
Eusebius highlights that the Holy Scriptures foretold specific "unmistakable signs" of Christ's coming. These signs included the abolition and complete destruction of the three outstanding offices of dignity among the Hebrews (kingship, prophet, and high priesthood), the cessation of Mosaic worship, the desolation of Jerusalem and its Temple, and the subjection of the entire Jewish race to its enemies. He asserts that these events were precisely fulfilled in the historical destruction of Jerusalem by the Romans shortly after Christ's appearance, serving as direct evidence that the prophesied "times had come" and that Jesus was indeed the Christ.
Eusebius defines these three as distinct forms of religion. Hellenism is characterized as the worship of multiple gods according to the ancestral religions of various nations (polytheism). Judaism is defined as the polity constituted according to the Law of Moses, dependent on the one, omnipotent God. Christianity, however, is presented as an ancient, natural, and venerable form of monotheistic religion that predates Moses. It is seen as a restoration of the piety practiced by pre-Mosaic saints like Abraham, Enoch, Noah, and Job, who worshipped the One God without adhering to the later Mosaic Law. Eusebius positions Christianity as a "third form of religion midway between Judaism and Hellenism," representing the most ancient and venerable philosophy now codified for all mankind through Christ.
Eusebius argues that Moses's enactments were specifically applicable only to the Jews living in their own land, particularly Judaea, and not to all nations or even to Jews dispersed among the Gentiles. He cites Mosaic laws requiring males to appear thrice a year in a specific chosen place (Jerusalem) for worship, and mandates for purification rituals (e.g., after childbirth or touching a corpse) that involved specific offerings at that same central location. He contends that it would be geographically and practically impossible for people from "the uttermost parts of the earth" to adhere to these requirements, thus proving the Mosaic Law's limited scope.
Eusebius explains that Christ did not "destroy" the Mosaic Law but "fulfilled" it. He argues that the Mosaic Law was a temporary measure, acting like a "nurse and governess of childish and imperfect souls" to lead the Jewish race away from polytheism back to the worship of the One God. However, it contained symbolic rituals and geographical restrictions that were impractical for a universal faith. Christ, as the "second Lawgiver," introduced a "new covenant" and "new law" (the Gospel) that focused on inward purity, spiritual worship (worshipping "in spirit and in truth" everywhere), and universal application to all nations. This new law completed and transcended the old, making its external observances superfluous after the destruction of the Temple and the Jewish kingdom.
Eusebius refers to Moses's prophecy in Deuteronomy (18:15, 19) about a prophet whom the Lord would raise up "like unto me." He argues that none of the later prophets after Moses were "like Moses" in the sense of being a Lawgiver, as they all directed their hearers back to Moses's law. Jesus Christ, however, came as a new Lawgiver for all nations, instituting a higher, more perfect law that superseded Mosaic ordinances. For instance, Christ's teachings on anger instead of murder, and desire instead of adultery, are presented as laws given with authority, fulfilling the prophecy of a prophet "like Moses" who would issue new divine commands.
Eusebius addresses these perceived discrepancies by arguing that circumstances have changed. Regarding procreation, the ancient "men of God" lived at the beginning of human history when the multiplication and flourishing of the human race were crucial. In contrast, Christians live in a world "nearing its end," where the emphasis is on spiritual matters and the establishment of God's kingdom. Furthermore, external distractions in the contemporary world make a focus on family potentially compete with religious devotion. For animal sacrifices, Eusebius states that while early men did offer animal sacrifices as a ransom for their lives, believing blood atoned for sin, this practice was a "symbol" or "likeness" anticipating a greater, "perfect" sacrifice. This perfect sacrifice is Christ himself, the "Lamb of God," whose blood atones for the sins of the world, making the old animal sacrifices obsolete. Christians now commemorate this ultimate sacrifice through a "bloodless, reasonable" offering of good works and pure hearts.
Eusebius describes two distinct ways of life within Christianity. The first is a "perfect form," which is "above nature" and "beyond common human living." This path involves abstaining from marriage, child-bearing, and material wealth, with individuals wholly dedicating themselves to the service of God with "heavenly love." They act as a "priesthood to Almighty God for the whole race" through virtuous deeds and pure intentions, offering "bloodless, reasonable" sacrifices. The second, "more humble, more human" way of life, permits marriage, child-bearing, engagement in government, farming, trade, and other secular interests alongside religious devotion. This "secondary grade of piety" provides support and guidance for the majority of people, ensuring that salvation and Gospel teaching are accessible to all, regardless of their societal roles.