As the disciples ran out into the streets that day, no doubt their faces were red with enthusiasm and excitement, as they proclaimed the gospel in many different languages. Red is the color that symbolizes the fire of the Holy Spirit, which inspires Christians to burn with passion for the sake of the Gospel of Jesus Christ. But fire is not the only thing that is red. Blood is red, too, as it flows from the injured bodies of the faithful whom the world is trying to destroy. Blood comes from wounds inflicted by a world that hates God.
Blood comes from martyrs.
When the Holy Spirit came to the disciples at Pentecost, it gave them great power and boldness in bearing witness to the Gospel of Jesus Christ. But the Holy Spirit also led to the arrest of Peter and John. It led to the arrest and flogging of apostles. It led to the death by stoning of Stephen. And eventually it led to such severe persecution against the Christians in Jerusalem that most of them had to flee the city.