Gregory the Great
Catena Aurea · Lukasevangelium 14
For which of you, intending to build a tower, sitteth not down first, and counteth the cost, whether he have sufficient to finish it? Lest haply, after he hath laid the foundation, and is not able to finish it, all that behold it begin to mock him, Saying, This man began to build, and was not able to finish. Or what king, going to make war against another king, sitteth not down first, and consulteth whether he be able with ten thousand to meet him that cometh against him with twenty thousand? Or else, while the other is yet a great way off, he sendeth an ambassage, and desireth conditions of peace. So likewise, whosoever he be of you that for-saketh not all that he hath, he cannot be my disciple.
(37. in Ev.) Because He had been giving high and lofty precepts, immediately follows the comparison of building a tower, when it is said, For which of you intending to build a tower does not first count &c. For every thing that we do should be preceded by anxious consideration. If then we desire to build a tower of humility, we ought first to brace ourselves against the ills of this world.