17A
Şرې Caitanya -caritāmrta
[[Madhva-lilā Ch 20]]
Vişṇu cannot be transformed into any form of material energy. Whenever there is association with  māyā , the personality involved must be different from Lord Vişṇu. Therefore Lord Śiva and Lord Brahmā are called  guṇa-avatāras , for they associate with the material qualities. The conclusion is that Rudra is a transformation of Vişṇu, but he is not exactly Lord Vişṇu. Therefore, he does not come within the category of the  viṣṇu-tattvas . Thus he is inconceivably one with Vişṇu and different from Him. The example given in this verse is very clear. Milk is compared to Vişṇu. As soon as milk touches a sour substance, it becomes yogurt, or Lord Śiva. Although yogurt is constitutionally milk it cannot be used in place of milk.
TEXT 3100
ক্ষীরং   যথা দ্বিধি বিকার বিশেষযোগ্য২
সংজ্ঞায়তে ন তৃ ততঃ পৃথগস্তি হেতোঃ।।
ব:  শম্ভতামণি তথা সমূপৈতি কাৰ্বাদ্
গোবিন্দমাদিপুরুষং তমহং ভক্রামি ॥ ৩১০
kṣīraṁ yathā dadhi vikāra-viśeṣa-yogāt sañjāyate na tu tataḥ pṛthag asti hetoḥ yaḥ śambhutām api tathā samupaiti kāryād govindam ādi-puruṣaṁ tam ahaṁ bhajāmi
SYNONYMS
kṣīram —milk;  yathā —as;  dadhi —yogurt;  vikāra-viśeṣa —with a special transforming agent;  yogāt —by mixing;  sañjāyate —is transformed into;  na —not;  tu —but;  tataḥ —from the milk;  pṛthak —separated;  asti —is;  hetoḥ —which is the cause;  yaḥ —who;  śambhutām —the nature of Lord Śiva;  api —even though;  tathā —as;  samupaiti —accepts;  kāryāt —from the matter of some particular business;  govindam —unto Govinda, the Supreme Personality of Godhead;  ādi-puruṣam —the original person;  tam —unto Him;  aham —I;  bhajāmi —offer my respectful obeisances.
TRANSLATION
“‘Milk changes into yogurt when mixed with a yogurt culture, but actually it is constitutionally nothing but milk. Similarly, Govinda, the Supreme Personality of Godhead, assumes the form of Lord Śiva [Śambhu] for the special purpose of material transactions. I offer my obeisances at His lotus feet.’
PURPORT
This is a quotation from  Brahma-samhitā  (5.45)...