Ven. Moggallâna's work

It is said that from the two main disciples of the Buddha, Ven.
Sâriputta performed the duty of teaching people until they could
attain Stream-entry, at which they would certainly become enlightened.
Ven. Moggallâna however, would continue to teach stream-enterers till
they attained arahant, at which they had reached the final stage of
enlightenment. Why did the Venerable continue to teach people who were
already destined for enlightenment? Why did he not teach newcomers,
whose minds were filled with impurities? Because he aimed at building
leaders of the Dhamma. If anyone had reached arahantship, he would be
able to devote his time in living and teaching that Dhamma he had
attained, and that would be for the benefit of many.

Sometimes it is better to perfect something already reasonably
well-done, than to do many things reasonably well.