1:13 and in the middle of the lampstands one like a son of man, clothed in a robe reaching to the feet, and girded across His breast with a golden girdle.
and in the middle of the lampstands one like a Son of Man,
The `Son of Man' was Jesus' favorite expression in referring to Himself. Paul describes how humbling this must have been for One to come from heaven's glory to assume the form of man as Jesus did - Philippians 2:3-8.
Now John sees Jesus 'like' the Son of Man...he still had a recognizable human form but somehow he was different. Perhaps that is why we get a description of the clothing of this Son of Man.
John uses this same expression for the One sitting on the cloud ready to harvest (pass judgment on) the earth - Revelation 14:14.
Note the location of this Son of Man. It is in the middle of His churches. He still is among His churches today not so much in the role of supplier of the church's needs but as the disciplinarian and judge. He is testing and trying the loyalty of His followers. See the comments this Son of Man makes about His churches in this Revelation.
clothed in a robe reaching to the feet,
The first article of clothing is His robe. Being fully clothed indicates absolute righteousness; recall that the one time His garments were taken from Him was when He was made naked for the cross - Matthew 27:27-36. He took the sins of the world upon Himself during that nakedness. This is why He could reprimand Laodicean church members about their nakedness - Revelation 3:18.
Furthermore, this fully robed Son of Man looks like the High Priest of Moses' time. See Exodus 28:2-5. Jesus Christ now is at the right hand of God, the Father, (Acts 7:51-60) standing there in absolute righteousness just as the High Priest was to do in performing his ceremonies.
This fully clothed Son of Man also speaks to the fact that the true inner nature of Jesus still is hidden. Jesus did not talk much of His role as Judge while He was on the earth...perhaps that is why this book is called the Revelation of Jesus Christ. It is appropriate that we see Him thusly clothed at the beginning of this book.
and girded across His breast with a GOLDEN GIRDLE.
There are two views (both supported by Scripture) as to what this symbolizes. First, in ancient times, the girdle was the symbol of strength and authority. Commoners wore tunics of loose-fitting clothing, but ones in authority wore the girdles. See the judgment carried out in Ezekiel 9.
The other view is that the girdle represents His righteousness and faithfulness (Isaiah 11:1-5) in carrying out judgment. This is exactly how the breastpiece of the High Priest is described - Exodus 28:15-21. The golden color denotes kingly judgment.