Revelation 3:4 - Matthew Poole's English Annotations on the Holy Bible

Thou hast a few names even in Sardis, a few persons even in that polluted place, which have not defiled their garments; who have kept their integrity and innocency. There is a garment of Christ's righteousness, which, once put on, is never lost, nor can be defiled; but there are garments of holiness also: hence the apostle calls to Christians to be clothed with humility. As sin is expressed under the notion of nakedness, so holiness is expressed under the notion of a garment, Ezekiel 16:10 1 Peter 5:5. Those who have not defiled their garments, are those that have kept a pure conscience. And they shall walk with me in white: the Romans used to clothe their nobles, and such as were competitors for honours, in white garments; the priests and Levites also amongst the Jews, when they ministered, were clothed in white, 2 Chronicles 5:12. God and his holy angels are in Scripture set out to us as clothed in white, Daniel 7:9 Matthew 17:2; Matthew 28:3. Those that triumphed upon victories obtained, were clothed in white amongst the Romans. To these usages, or some of them, the allusion is, and the meaning is, they shall be to me as kings, and priests, and nobles, they shall be made partakers of my glory: for they are worthy; though they have not merited it, yet I have judged them worthy; they are worthy, though not with respect to their merit, yet with respect to my promise.