Bathunō (βαθύνω) means "to deepen, to dig deep, to make profound." It appears once in the NT in Luke 6:48, in the parable of the two builders: the wise builder "dug deep [eskapsen kai ebathynen]" and laid his foundation on rock, so that when the flood came the house stood firm.
The wise builder's act of bathunō — digging deep — is the image of deliberate, costly spiritual formation. Building on rock requires effort, time, and downward movement before any upward structure appears. The house that stands in the flood is built by one who heard Christ's words AND did them (Luke 6:47). Spiritual depth is not achieved by surface-level religious activity but by sustained, disciplined engagement with the Word of God — going down into it, letting it transform at the foundation level. Christ is the foundation (1 Corinthians 3:11); digging to Him is the work of genuine discipleship.