So also the chief priests with the scribes mocked him to one another, saying "He saved others; he cannot save himself. Let the Christ, the King of Israel, come down from the cross that we may see and believe."
Only by Jesus staying on the cross and bearing the wrath of God in the place of sinners like the chief priests and scribes could they and us ever believe. If Jesus came down from the cross there would be no hope for us to believe in Him because apart from being made alive together with Christ we are dead in our sins and trespasses and unable to see and believe in Him as our Savior and Treasure.
And so by God's grace, Jesus Christ stayed on the cross and there purchased the New Covenant in His blood which purchased for believers the grace of repentance and faith of seeing and believing. (Jeremiah 31:3; Luke 22:20; Hebrews 13:20-21)
Oh how grateful we should be that Jesus did not come down from the cross, but stayed there for all who the Father had given him, all who will believe in Him.