In Things Fall Apart, what do the outcasts have to do to be accepted into the church?

In order to join the Christian church, the outcasts must shave off their hair.

According to tribal custom, the outcast, or osu, is

"a person dedicated to a god, a thing set apart - a taboo for ever, and his children after him. He (can) neither marry nor be married by the free-born. He (is) in fact an outcast, living in a special area of the village...Wherever he (goes) he carrie(s) with him the mark of his forbidden caste - long, tangled and dirty hair."

The outcasts believe that if they shave their heads, they will die. When, seeking acceptance, some of them begin to attend services at the Christian church, the missionary interpretor, Mr. Kiaga, welcomes them, but the other converts protest. Mr. Kiaga, however, stands firm, and tells the outcasts that if they "shave off the mark of (their) heathen belief," their hair, they will be welcomed into the church. When they express their terror at the thought of violating the taboo, Mr. Kiaga exhorts them, saying,

"How are you different from other men who shave their hair? The same God created you and them. But they have cast you out like lepers...The heathen say you will die if you do this or that, and you are afraid. They also said I would die if I built my church on this ground. Am I dead? They said I would die if I took care of twins. I am still alive. The heathen speak nothing but falsehood. Only the word of our God is true."

Heartened by Mr. Kiaga's assurance, the outcasts shave off their hair, and soon become among "the strongest adherents of the new faith (Chapter 18).