For which of you, intending to build a tower, sitteth not down first, and counteth the cost, whether he have sufficient to finish it? To build a tower - Probably this means no more than a dwelling house, on the top of which, according to the Asiatic manner, battlements were built, both to take the fresh air on, and to serve for refuge from and defense against an enemy. It was also used for prayer and meditation.
This parable represents the absurdity of those who undertook to be disciples of Christ, without considering what difficulties they were to meet with, and what strength they had to enable them to go through with the undertaking. He that will be a true disciple of Jesus Christ shall require no less than the mighty power of God to support him; as both hell and earth will unite to destroy him.