Note 5 at 1 Cor. 12:17: Now Paul changes the analogy to illustrate how ridiculous it would be if there weren't different gifts in the body of Christ. We wouldn't like it if our body was one big eye or one big ear. Likewise, if every member of the body of Christ had the same gift, it would not be good. We need all the different gifts.

If the only gift that functioned in the church was the evangelist, how would the new converts ever grow without the pastor or teacher? If every one had the gift of interpretation (see note 29 at 1 Cor. 12:10, p. 931), who would give the message in tongues (see note 28 at 1 Cor. 12:10, p. 931) He is saying diversity is good if the different gifts can appreciate each other and work together.