Shoghi Effendi - successor

O ye beloved of the Lord! It is incumbent upon the Guardian of the Cause of God to appoint in his own life-time him that shall become his successor, that differences may not arise after his passing. He that is appointed must manifest in himself detachment from all worldly things, must be the essence of purity, must show in himself the fear of God, knowledge, wisdom and learning. Thus, should the first-born of the Guardian of the Cause of God not manifest in himself the truth of the words: -- "The child is the secret essence of its sire," that is, should he not inherit of the spiritual within him (the Guardian of the Cause of God) and his glorious lineage not be matched with a goodly character, then must he, (the Guardian of the Cause of God) choose another branch to succeed him.

‘Abdu’l-Bahá, The Will and Testament, p. 12