Jesus had already said in Revelation 3:4 that the faithful few would be dressed “in white.” The repetition serves to underline this wondrous promise in the minds of those few faithful Christians in Sardis as they feel the pressure of being a distinct minority. Their conquering, though it may take blood, sweat, and tears, will be worth it.
5 The one who conquers will be clothed thus in white garments, and I will never blot his name out of the book of life. I will confess his name before my Father and before his angels.