B.G 4.11
ये यथा मां प्रपद्यन्ते तांस्तथैव भजाम्यहम्। मम वर्त्मानुवर्तन्ते मनुष्याः पार्थ सर्वशः ॥११॥
yē yathā māṁ prapadyantē tāṁstathaiva bhajāmyaham। mama vartmānuvartantē manuṣyāḥ pārtha sarvaśaḥ ॥11॥
As they worship Me, accordingly I reciprocate to them. O Arjuna, humans are subsurvient to my ways in all aspects.
Gīta Tātparya 4.11
"tathaiva bhajāmi" = I give results accordingly. Even the worship of other deities must ultimately be dedicated to Lord Vishnu in order to yield results.
The words "tathaiva bhajāmi" mean "I give results accordingly". Even the worshippers of other deities dedicate to me only, but following directly Vaishnavism produces better results.
"Even the worship of other deities becomes the cause of heaven and other rewards, only when they are dedicated to lord Vishnu in the end, not otherwise."
-states Agni Purana.