原文 Original text
繁體 Traditional
Reader's edition
信心從願 The Old Prince Consents Gladly
此誠莫大之功，不知父王以為何如？」老王聞言，信心從願。此诚莫大之功，不知父王以为何如？」老王闻言，信心从愿。
逐句解 Line by line
此誠莫大之功，不知父王以為何如？」
此诚莫大之功，不知父王以为何如？」
This would truly be a merit beyond measure. We do not know what our father thinks of it."
They close on the same phrase they opened with, 莫大之功, a merit beyond measure, so it brackets the whole speech. 為 is wéi in 以為, to consider — and having made their case they hand the decision back, correctly, to the man who has to make it.
老王聞言，信心從願。
老王闻言，信心从愿。
The old prince heard them out and gave his belief and his consent.
Eight characters for a decision that changes the rest of the chapter. 信心 is faith or confidence — here, believing what he has been told — and 從願 is to go along with what is wished. He does not argue, test, or ask to see for himself. His sons tell him and he believes them.
Two lines, and one of them is the answer. The old prince is given the chapter's only real decision and takes it in eight characters.
What he does not do is the interesting part. He does not summon the disciples for an examination, or consult anybody, or sleep on it. This is the same man who stamped a fourteen-year-old travel document without a quibble, and the chapter has been consistent about him from the start.