Bhagavad Gita 9.15 is Chapter 9, Verse 15, in Raja Vidya Raja Guhya Yoga (Royal Knowledge). Below are the Sanskrit text, a transliteration, a plain-English translation and an explanation.
jñāna-yajñena cāpy anye yajanto mām upāsate ekatvena pṛthaktvena bahudhā viśvato-mukham
"Others worship Me through the sacrifice of knowledge, seeing Me as one, as separate, as many, as the universal form facing everywhere."
What This Means:
Not everyone worships through devotion; some worship through knowledge (jnana-yajna). They see Krishna as One (non-dual), or as separate (dualistic), or as many forms, or as the universal presence everywhere.
Going Deeper:
Krishna accepts diverse approaches. Some see unity, some see distinction, some see multiplicity, all are valid. The important thing is that they're seeking HIM, however they conceive Him.
How To Apply This:
Your particular understanding of the Divine is valid if it leads you toward truth. Don't worry if others see it differently. Multiple maps can lead to the same territory.
Key Sanskrit Terms: