What's the wisdom behind Umar bin al khattab asking Owais al qarni for dua?

The prophet informed Umar bin al khattab to request Owais al qarni to pray to Allah for forgiveness of Umar. Sunni corpus affirms Umar is second best person of this ummah. What's the wisdom behind prophet informing Umar to place the request given Umar had been already given glad tidings of Paradise by the prophet himself? https://abdurrahman.org/2009/07/23/the-story-of-uwais-al-qarni/