In which in addition to him staying with them, for a period of time, seeing Tsuki's potential, they proposed that he stay with them for six months, long enough for them to share their knowledge, in which they would have Tsuki as the his apprentice, so he could take his teachings with him.
In which in addition to sharing in the priests' house, in which they could be his mediator and representative, contact and mediator at Um-Mu's headquarters, so Tsuki fulfilling the promise, in addition to learning, he would have to go back to the headquarters, with the sacred object.