BernSt. Bernard of Clairvaux from Commentary on the Song of Songs (Sermon 1):

We must conclude then it was a special divine impulse that inspired these songs of his that now celebrate the praises of Christ and his Church, the gift of holy love, the sacrament of endless union with God. Here too are expressed the mounting desires of the soul, its marriage song, an exultation of spirit poured forth in figurative language pregnant with delight. It is no wonder that like Moses he put a veil on his face, equally resplendent as it must have been in this encounter, because in those days few if any could sustain the bright vision of God’s glory. Accordingly, because of its excellence, I consider this nuptial song to be well deserving of the title that so remarkably designates it, the Song of Songs, just as he in whose honor it is sung is uniquely proclaimed King of kings and Lord of lords.

Source: Glorify His Name