What does the Bible say about the happiest day for believers?

According to Psalm 17:15, the happiest day for a believer is when they close their eyes in death and behold the face of Christ in righteousness. This is when they will be fully conformed to Christ's likeness, satisfying the deepest longings of their soul. Paul reinforces this hope in 1 Corinthians 2:9, highlighting that no eye has seen nor ear has heard what God has prepared for those who love Him. This assures believers that their ultimate fulfillment and joy await them in the reality of Christ's presence.