The Saviour mentions three blessings that will be given to overcomers and each of the blessings is connected to the Day of Judgement. One of the blessings, that of wearing white robes, refers to what took place when people celebrated great victories. They would wear white garments of triumph.
In the previous verse, Jesus had stated that the faithful few in Sardis would walk with him in white, which is probably a reference to victory parades when loyal soldiers would be given the great privilege of accompanying the triumphant leader as he led the celebrations. Spiritual overcomers are going to share the victory of the King. Of course, they will give him all the praise, and we know that he will deserve eternal honour. Nevertheless, several times in Revelation God’s people are described as clothed in white robes as they rejoice in the triumphs of Jesus (7:9-10; 19:14).
The second blessing is guaranteed residence of the heavenly city. Ancient cities had registers containing the names of the residents. Of course, the register was only as viable as the competence of the rulers to ensure the existence of their cities. If they could not, and Sardis had known such failures, having their names recorded was of little worth. In contrast, those whose names are written in the register of heaven will enjoy it forever.
It seems that a resident of Sardis who received the death penalty would have his name deleted from the city register. Perhaps Jesus is indicating that some of his people there would experience that in the future when they were martyred. Yet even if their names were removed from the register in Sardis, they would not be taken out of the book of life. Their eternal security did not depend on anything on earth.
The third blessing is that Jesus will confess their names before his Father and the angels. Perhaps the idea is that he is reading out the names in the book and indicating their place in his city. It is a beautiful picture of the sovereign and his subjects. Confession by definition is public, and here Jesus promises to state publicly that they are his people. Perhaps the best sound they will ever hear.