The Oldest Existing Christian Hymn

The Oxyrhynchus hymn is the oldest existing Christian hymn that we have the notes for, dating from the second or third century AD. We have the words to older hymns but we really do not know how the melody went. It is also interesting that this hymn was found in a old dump near Egypt. Here are the words to the hymn which are beautiful:

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...Let it be silent,Let the Luminous stars not shine, Let the winds and all the noisy rivers died down; And as we hymn the Father, the Son and the Holy Spirit, Amen Let all the powers add "Amen Amen"praise always, and glory to God,Amen Amen The sole giver of good things, Amen Amen.
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As for indirect apologetics it is note worthy to point out that it is a hymn to the Trinity.

Here is some links one of which has audio of how the hymn sounded.

Oxyrhynchus hymn Audio
Oxyrhynchus hymn