Adam Clarke on Revelation 3:4

Thou hast a few names even in Sardis - A few persons, names being put for those who bore them. And as the members of the Church were all enrolled, or their names entered in a book, when admitted into the Church or when baptized, names are here put for the people themselves. See Rev 3:5.

Have not defiled their garments - Their souls. The Hebrews considered holiness as the garb of the soul, and evil actions as stains or spots on this garb. So in Shabbath, fol. 152, 2: "A certain king gave royal garments to his servants: those who were prudent folded them up, and laid them by in a chest; those who were foolish put them on, and performed their daily labor in them. After some time the king asked for those royal robes; the wise brought theirs white and clean, the foolish brought theirs spotted with dirt. With the former the king was well pleased; with the latter he was angry. Concerning the former he said: Let those garments be laid up in my wardrobe, and let the persons go home in peace. Of the latter he said: Let the garments be put into the hands of the fuller, and cast those who wore them into prison." This parable is spoken on these words of Ecclesiastes, Ecc 12:7 : The spirit shall return to God who gave it.

They shall walk with me in white - They shall be raised to a state of eternal glory, and shall be for ever with their Lord.