大毘盧遮那成佛經疏 3.37

3.37

「究習瑜伽」者，謂善修相應法也。謂於三部真言上中下成就等事一一通達，皆與正理相應，名善修瑜伽。又於息災法中，即能以此方便增益、降伏。或增益法中，即能以此方便降伏、息災。於降伏法中，即能以此方便息災、增益。隨彼彼相應之法，皆能善分別之，名善修瑜伽。又於漫荼羅中，種種本尊三昧、形色、字印、性類、威儀，及供養成就時，運心觀察方便，皆已相應修習，此中障礙及悉地相亦善覺知，乃可傳法也。復次大悲胎藏發生三昧中，有種種法界門、種種善知識，如善財童子次第詢求。或於如是法門已善修行，而於餘門未能究習，若入普門世界時，則能於一念中具足相應，是名深行阿闍梨也。

Regarding "thoroughly practicing yoga": this means properly cultivating the dharmas of union (yoga). That is, fully penetrating every detail of superior, middling, and inferior accomplishments in the mantras of the three divisions, all according with the correct principle—this is called properly cultivating yoga. Furthermore, within the pacification rites (śāntika), one can use this upāya for enrichment (pauṣṭika) and subjugation (ābhicāruka). Or within enrichment rites, one can use this upāya for subjugation and pacification. Within subjugation rites, one can use this upāya for pacification and enrichment. One is able to skillfully distinguish whatever corresponding dharmas apply; this is called properly cultivating yoga. Moreover, within the maṇḍala, the samādhis, forms, colors, seed-syllables, seals, natures, classes, and deportments of the various tutelary deities, as well as the upāya of directing the mind in contemplation during the accomplishment of offerings, are all cultivated in union; he also clearly perceives the obstacles and signs of siddhi therein. Only then may he transmit the Dharma. Furthermore, within the samādhi of the arising of the mahākaruṇāgarbha, there are various entrances to the dharmadhātu and various spiritual friends, just like the youth Sudhana seeking them out one after another. If one has skillfully practiced such Dharma gateways but has not yet thoroughly practiced other gateways, yet upon entering the universal gateway world (samantamukha) one is able to fully accord in a single thought-moment—this is called an ācārya of profound practice.