Basil of Caesarea

For perhaps He delays purposely, to redouble your earnestness and coming to him, and that you may know what the gift of God is, and may anxiously guard what is given. For whatever a man acquires with much pains he strives to keep safe, lest with the loss of that he should lose his labour likewise.

Catena Aurea by Aquinas ↗

Theophylact of Ohrid

"Importunity" he calls the intense and prolonged prayer with patience. Understand it also in another way, namely: by "midnight" understand the force and the middle of temptations. For every temptation is a night, and the middle of temptations is, without doubt, midnight. So when someone is in the middle of temptations, he comes to God Who loves us and says: "lend me three loaves," that is, the salvation of body, soul, and spirit. For temptations threaten danger to these three. And who is the "friend" who has come off the road? …

Commentary on Luke ↗

Bede

And if he persists in knocking, I tell you, even if he will not give him rising because he is his friend, still because of his impudence, he will rise and give him as many as he needs. And I tell you: Ask, and it will be given to you. Seek, and you will find. Knock, and it will be opened to you. It is a comparison from the lesser. For if a human friend rises from bed and gives not out of friendship but compelled by weariness, how much more will God give, who grants generously without weariness what is asked? …

On the Gospel of Luke ↗

Bonaventure

Third, regarding compelling importunity, he adds: And if he shall continue knocking, with prayers, not overcome by shame nor wearied by tedium nor broken by despair, as a true friend, according to that passage in Ecclesiasticus 22: "If you have drawn a sword against a friend, do not despair; for there is a way back to a friend. And if you have opened a sorrowful mouth, do not fear". …

Commentary on Luke, Chapter 11 ↗