This is the only extant letter we have from Polycarp. Polycarp was the bishop of Smyrna, a city in Greece, who was martyred for the faith. Irenaeus and Tertullian tell us that Polycarp was a disciple of John.

The letter was written in the early second century. It reads similarly to letters we see in the New Testament. Encouragement, exhortations to holiness, and warnings against false teaching and apostasy are found throughout.

He begins the letter saying, “Polycarp, and the presbyters with him, to the Church of God sojourning at Philippi:” I suppose this could be read any number of ways, but regarding church polity we see that Polycarp is ruling with a plurality of presbyters.

Later, Polycarp appears to be pushing against the Docetic heresy. Those who denied that Christ came in the flesh. He says, “‘For whosoever does not confess that Jesus Christ has come in the flesh, is antichrist;’ [1 John 4:3] and whosoever does not confess the testimony of the cross, is of the devil; and whosoever perverts the oracles of the Lord to his own lusts, and says that there is neither a resurrection nor a judgment, he is the first-born of Satan.” – Chapter 7. Avoid the Docetæ, and persevere in fasting and prayer

It makes sense that Polycarp being a disciple of John would warn of such things, since John also warns against these things.

Lastly, he talks about a former elder named Valens who had apostatized.

“I am greatly grieved for Valens, who was once a presbyter among you, because he so little understands the place that was given him…I am deeply grieved, therefore, brethren, for him (Valens) and his wife; to whom may the Lord grant true repentance! And be then moderate in regard to this matter, and do not count such as enemies, 2 Thessalonians 3:15 but call them back as suffering and straying members, that you may save your whole body. For by so acting you shall edify yourselves.” – Chapter 11. Expression of grief on account of Valens

This is a great word to the Philippians. To be moderate toward this lapsed leader, to not count him as an enemy, but to call him back as a straying member. Desirous of saving the whole body. Excellent.