Ambrose of Milan
Catena Aurea · Lukasevangelium 11
When the unclean spirit is gone out of a man, he walketh through dry places, seeking rest; and finding none, he saith, I will return unto my house whence I came out. And when he cometh, he findeth it swept and garnished. Then goeth he, and taketh to him seven other spirits more wicked than himself; and they enter in, and dwell there: and the last state of that man is worse than the first.
For Israel being adorned with a mere outward and superficial beauty, remains inwardly the more polluted in her heart. For she never quenched or allayed her fires in the water of the sacred fountain, and rightly did the unclean spirit return to her, bringing with him seven other spirits more wicked than himself. Hence it follows, And he goeth and taketh with him seven other spirits more wicked than himself, and they enter in and dwell there. Seeing that in truth she has sacrilegiously profaned the seven weeks of the Law, (i. e. from Easter to Pentecost,) and the mystery of the eighth day. Therefore as upon us is multiplied the seven-fold gifts of the Spirit, so upon them falls the whole accumulated attack of the unclean spirits. For the number seven is frequently taken to mean the whole.