The central message of this sermon is that true spiritual transformation and understanding of God's kingdom require a radical rebirth, which Jesus refers to as being "born again." This phrase, often used in popular culture to describe a superficial or external change, has been watered down and lost its original meaning. According to the sermon, being born again means being transformed from within by the power of the Holy Spirit, rather than just undergoing an external change or adopting a new label. The takeaway is that spiritual renewal and understanding of God's kingdom require a deep inner transformation, which cannot be achieved through human effort or external measures alone.