You need to know about this because a common refrain of some critics of the faith is that major Christian doctrines were not present in the earliest years of the church. They were accoutrements that developed over time. The full divinity of Jesus? Not till Nicea. A substitutionary atonement? Not until Anselm rigged the jury in the middle ages.
There are of course many ways to respond to this. One way that Dr. Michael Kruger has pointed out is to appeal to the Epistle to Diognetus, a second century work of Christian apologetics. It’s clear that the author of this Epistle had a high Christology and affirmed a robust view of substitionary atonement and even imputation.
No early evidence of the divinity of Jesus? Consider this:
But the truly all-powerful God himself, creator of all and invisible, set up and established in their [Christians’] hearts the truth and the holy word from heaven, which cannot be comprehended by humans. To do so, he did not, as one might suppose, send them one of his servants or an angel or a ruler…but he sent the craftsman and maker of all things himself, by whom he created the heavens, by whom he encloses the sea within its own boundaries, whose mysteries all the elements of creation guard faithfully, from whom the sun was appointed to guard the courses that it runs during the day, whom the moon obeys when he commands it to shine at night, whom the stars obey by following the course of the moon, by whom all things are set in order and arranged and put into subjection, the heavens and the things in the heavens, the earth and the things in the earth, the sea and all the things in the sea, fire, air, the abyss, creatures in the heights, creatures in the depths, and creatures in between–this is the one he sent to them. (7.2)
So, then, did he [God], as one might suppose, send him [his Son] to rule in tyranny, fear, and terror? Not at all. But with gentleness and meekness, as a king sending his own son, he sent him as a king; he sent him as God; he sent him as a human to humans. So that he might bring salvation. (7.3-4).
The Word appeared to them [the apostles] and revealed things, speaking to them openly. Even though he was not understood by unbelievers, he told these things to his disciples, who after being considered faithful by him came to know the mysteries of the Father. For this reason he sent his Word, that it might be manifest to the world. This Word was dishonored by the people but proclaimed by the apostles and believed by the nations. For this is the one who was from the beginning who appeared to be recent but was discovered to be ancient, who is always being born anew in the hearts of the saints. This is the eternal one who “today” is considered to be the Son, through whom the church is enriched and the unfolding grace is multiplied among the saints. (11:2-4).
But [God] was patient, he bore with us, and out of pity for us took our sins upon himself. He gave up his own Son as a ransom for us, the holy one for the lawless, the innocent one for the wicked, the righteous one for the unrighteous, the imperishable one for the perishable, the immortal one for the mortal. (9.2).
For what else could hide our sins but the righteousness of that one? How could we who were lawless and impious be made upright except by the son of God alone? Oh the sweet exchange!…That the lawless deeds of many should be hidden by the one who was upright, and the righteousness of one should make upright the many who were lawless!
If you read the comments section of the post, there’s a fairly developed interaction between Dr. Kruger and a commenter named John S that some might find helpful if they want to see this point developed further.