Vows 12 and 13 come after Vow 11, which vows to unfailingly have anyone who dies a peaceful death in the Pure Land become a Buddha, and thus it refers to the virtue they should possess.
第十一願の往生浄土する者を必ず成仏せしめるという誓いの後の第十二・十三願であるから、往生浄土したものに具わるべき徳。