'To build a tower,' as in Luke 14:27, signifies acquiring interior truths.

In Genesis 11:4, this signifies the worship of self, which consists of a person exalting himself above others, even to the point of worship. This is why self-love, which is arrogance and pride, is called 'height,' 'loftiness,' and 'lifting up,' and is described with anything high. Self-love in worship, or the worship of self is called 'a tower,' because 'a city' signifies doctrine, and ancient cities were fortified with towers with guards.

Towers were also built on the borders of a country. This is why they were called guard towers, or watchmen in 2 Kings 9:17, 17:9, 18:8, and watch-towers, in Isaiah 23:13.

(References: Arcana Coelestia 1306; Isaiah 1, 5, 5:1-2; Luke 14; Mark 1, 12:1, 12; Matthew 21, Matthew 21:33)