Mateo 18:3

Except ye turn and become

(εαν μη στραφητε κα γενησθε). Third-class condition, undetermined but with prospect of determination. Στραφητε is second aorist passive subjunctive and γενησθε second aorist middle subjunctive. They were headed in the wrong direction with their selfish ambition. "His tone at this time is markedly severe, as much as when He denounces the Pharisaism in the bud He had to deal with" (Bruce). The strong double negative ου μη εισελθητε means that they will otherwise not get into the kingdom of heaven at all, let alone have big places in it.