What does the Bible say about happiness in Christ?

In the sermon, it is emphasized that true happiness cannot be found in fleeting desires or the things of the flesh. Rather, joy is derived from knowing that our names are written in the Lamb's Book of Life, which signifies our salvation and eternal security. The Lord Jesus Christ highlights that joy comes not from worldly successes or approval but from a deep relationship with Him, as seen in Luke 10:20, where He instructs His disciples to rejoice for their names are recorded in heaven. This teaching reflects the sovereign grace of God who saves His people, confirming that true fulfillment is in serving Christ's cause.