John the Apostle
Revelation 3:13ESV·traditional attribution

He who has an ear, let him hear what the Spirit says to the churches.’

Matthew Henry Presbyterian @wholebiblehenry

We have now come to the sixth letter, sent to one of the Asian churches, where observe, I. The inscription, showing, 1. For whom it was more immediately designed: The angel of the church of Philadelphia; this also was a city in Asia Minor, seated upon the borders of Mysia and Lydia, and had its name from that brotherly love for which it was eminent.

Commenting on Revelation 3:7-13

John Gill Reformed Baptist @doctorgill

I know thy works,.... Which were far from being perfect, and not so good as those of the former church: that thou art neither cold nor hot; she was not "cold", or without spiritual life, at least in many of her members, as all men by nature are, and carnal professors be; she was alive, but not lively: nor was she wholly without spiritual affections...

William Burkitt Anglican @expositoryburkitt

This is again the close and conclusion of this, as it was before of all the epistles, in which Christ calls upon all persons to hear and consider what he saith by his Spirit to this church, and to lay it deeply to heart for their instruction and admonition.