I think bodhiruchi is asking which Vow of the 48 Vows is the most emphasised in Jodo Shinshu.
Answer:
For Shinran Shonin, Five Vows are seen as important. The 11th, 12th, 13th, 17th and 18th.
(11) If, when I attain Buddhahood, humans and devas in my land should not dwell in the Definitely Assured State and unfailingly reach Nirvana, may I not attain perfect Enlightenment.
(12) If, when I attain Buddhahood, my light should be limited, unable to illuminate at least a hundred thousand kotis of nayutas of Buddha-lands, may I not attain perfect Enlightenment.
(13) If, when I attain Buddhahood, my life-span should be limited, even to the extent of a hundred thousand kotis of nayutas of kalpas, may I not attain perfect Enlightenment.
(17) If, when I attain Buddhahood, innumerable Buddhas in the land of the ten quarters should not all praise and glorify my Name, may I not attain perfect Enlightenment.
(1
If, when I attain Buddhahood, sentient beings in the lands of the ten quarters who sincerely and joyfully entrust themselves to me, desire to be born in my land, and call my Name, even ten times, should not be born there, may I not attain perfect Enlightenment. Excluded, however, are those who commit the five gravest offenses and abuse the right Dharma.
(from
http://www12.canvas.ne.jp/horai/48vows.htm)
These Five Vows correspond to the first five chapters of the Kyogyoshinsho. True Practice - 17, True Shinjin - 18, True Realization - 11, True Buddha and Buddha-land - 11 & 12.
Also, three Vows correspond to sentient being's birth in the Pure Land. Vows 18, 19 and 20.
(1
If, when I attain Buddhahood, sentient beings in the lands of the ten quarters who sincerely and joyfully entrust themselves to me, desire to be born in my land, and call my Name, even ten times, should not be born there, may I not attain perfect Enlightenment. Excluded, however, are those who commit the five gravest offenses and abuse the right Dharma.
(19) If, when I attain Buddhahood, sentient beings in the lands of the ten quarters, who awaken aspiration for Enlightenment, do various meritorious deeds [268b] and sincerely desire to be born in my land, should not, at their death, see me appear before them surrounded by a multitude of sages, may I not attain perfect Enlightenment.
(20) If, when I attain Buddhahood, sentient beings in the lands of the ten quarters who, having heard my Name, concentrate their thoughts on my land, do various meritorious deeds and sincerely transfer their merits towards my land with a desire to be born there, should not eventually fulfill their aspiration, may I not attain perfect Enlightenment.
However, in Shinran Shonin's view, Vows 19 and 20 are for those of: self-power practices - 19; and self-power nembutsu - 20. These two vows are skilful means (Upaya) to lead us to the Vow that enables us to be born in the True Fulfilled Land - Vow 18.
Gassho