God calls, and that’s what we see in the vocation of the great leaders. In our tradition, a mission always starts with a calling.
During the formation process, one must purify the right intention, because nobody, not even those who discover themselves called, responds with complete integrity; the response is a mixture because we are all sinners.
[H]e that wants to be a leader of the people of God has to give God His space; therefore to shrink, to recede into oneself with doubt, with the interior experience of darkness, of not knowing what to do, all of that ultimately is very purifying.
--Pope Francis, On Heaven and Earth, passim
Image source: Henry Ossawa Tanner, The Good Shepherd, http://blog.baejoseph.com/2012/11/an-essay-on-psalm-23.html