At the Council of Clermont, in 1095, Urban II preached (this is a BNF miniature from 1490) a sermon on the need to protect the Holy Land. Five accounts of his sermon survive. Each was written by a chronicler who was there.
His homily - more like a speech than a sermon - was clear in its directive and passionate in its tone. After chiding the knights against fighting each other, which they routinely did, Urban (quoted by Fulcher of Chartres) said:
For your brethren who live in the east are in urgent need of your help, and you must hasten to give them the aid which has often been promised them. For, as the most of you have heard, the Turks and Arabs have attacked them and have conquered the territory of Romania [the Greek empire] as far west as the shore of the Mediterranean and the Hellespont, which is called the Arm of St. George. They have occupied more and more of the lands of those Christians, and have overcome them in seven battles. They have killed and captured many, and have destroyed the churches and devastated the empire. If you permit them to continue thus for awhile with impurity, the faithful of God will be much more widely attacked by them.
After describing the problem, Urban II next uses persuasive words, and concepts, to spur his audience (mostly Frenchmen - called "Franks" at the time) into action:
On this account I, or rather the Lord, beseech you as Christ's heralds to publish this everywhere and to persuade all people of whatever rank, foot-soldiers and knights, poor and rich, to carry aid promptly to those Christians and to destroy that vile race from the lands of our friends. I say this to those who are present, it is meant also for those who are absent. Moreover, Christ commands it.
Who could argue against such authority?