4 Hence in this manner it behooved the Holy Spirit to be manifested when coming upon the Lord, that every one might understand that if he has the Holy Spirit he ought to be simple as the dove, to have true peace with his brethren, that peace which the kisses of doves signify. Ravens have their kisses too; but in the case of the ravens it is a false peace, in that of the dove a true peace. Not every one, therefore, who says, “Peace be with you,” is to be listened to as if he were a dove.
How then are the kisses of ravens distinguished from those of doves? Ravens kiss, but they tear; the nature of doves is innocent of tearing. Where consequently there is tearing, there is not true peace in the kisses. They have true peace who have not torn the Church. Ravens feed upon carrion, it is not so with the dove; it lives on the fruits of the earth, its food is innocent. This, brethren, is really worthy of admiration in the dove. Sparrows are very small birds, but yet they kill flies at least.
The dove does nothing of this sort, for it does not feed on what is dead. They who have torn the Church feed on the dead. God is mighty; let us pray that they who are devoured by them, and perceive it not, may come to life again. Many acknowledge that they do come to life again, for at their coming we daily express joy with them in the name of Christ. Be simple, but only in such wise that you be fervent, and let your fervor be in your tongues. Hold not your peace, speak with glowing tongues, set those that are cold on fire.
Source: Tractates on the Gospel of John (New Advent)