Why does the pastor wear a robe on Sundays?
When you walk into a church there are many signs that tell you that you are in a church. Candles, altar, crucifix, pulpit..These "churchy" things teach us a reality that we only behold by faith, this is a holy place. It is the very house of God.The church is the place where holy work is done.
The "holy-ing" though is not through us doing things but in receiving from Christ the gifts of forgiveness. Christ gives us his forgiveness in specific ways so that no matter how unholy we have been during the week, we know when we come to church it is not to make ourselves right with God, but we come for Christ to declare us forgiven. Christ does this in a specific way, through his Word. This Word is his word, not ours. It is not the opinion of a man or a nice moral lesson that teaches us how to be good disciples. Although that is important, our sins are not forgiven by our actions. Christ speaks to us.
Christ is with us through the preaching of his word. This is the calling that a pastor is given. He is to stand in the place of Christ and preach the faith once delivered to the saints. For faith comes from hearing the word of Christ. So how do we show that the pastor is not a man who is just teaching us his opinion or some vision that he made up? How do we show that it doesn't matter who the man is but what is important is what he preaches? We make the man disappear as much as possible. We cover everything individualistic about the man himself so that what he preaches may shine forth as a continuation of what the apostles themselves taught.
We come to the church to meet Christ, not a motivational speaker. Not a man who is "better than everyone else." The robe and all the other vestments cover up as much as possible the individual. Let's be honest, our sinful nature does not like this. We want to be the center of attention. The vestments(alb, cassock, surplice) force the man who is preaching to acknowledge he is not the center of attention, his(Christ's) preaching is. Every pastor who stands up to preach wears vestments. A suit is a vestment. A t-shirt is a vestment. A sports jersey is a vestment. Those things though allow you as a preacher to claim some amount of individuality. The church's vestments make the man disappear. It is humbling, but very freeing. "For I decided to know nothing among you except Christ and him crucified."