Paul uses the metaphor of childhood to describe a state of spiritual immaturity, where individuals are bound by the 'elemental spiritual forces of the world.' This can be understood as being trapped by basic, worldly principles and systems that do not lead to true freedom. Before coming to faith in Christ, people often find themselves adhering to legalistic or ritualistic practices, much like children who are not yet mature enough to make their own decisions.
This verse reflects the idea that without the guidance of faith, people are enslaved to these worldly elements, unable to experience the full freedom and maturity that comes with knowing Christ. The imagery of being 'underage' suggests a period of growth and learning, where one is not yet fully aware of the spiritual truths available through a relationship with God. Paul encourages believers to move beyond these constraints, embracing the liberty and maturity that faith in Christ offers, and to live in the freedom of being God's children.