Verse 4.4: Arjuna said: The sun-god Vivasvān is senior by birth to You. How am I to understand that in the beginning You instructed this science to him?
In order to clarify doubt and truly understand something, two things are required:
One needs to inquire from the right person.
It's a two way street, although a strong case can be made that most of the responsibility falls on the one who is posing the question. That's because they are the ones who:
1) Have to formulate the appropriate question or else they might not get the answer they need.
2) Have the free will to choose (and accept) the person to get answers from.
Let's use a real life example to understand that a bit better. If you've ever been to a foreign country, you might have first hand experience of trying to get to a destination and having no clue where to go. In stopping someone on the street, the first question you might ask is not how to get to x, y, z destination but... "Are you from here?"
That question is an important one as it helps you (the tourist) to find out if you're asking a reputable source (i.e. one who is qualified to answer). Well...at least in my experience, it may help but doesn't necessarily guarantee that you will get the directions you require!
But that qualifying question is an important one. It's easy to get answers to questions...
The difficulty lies in finding the right individual who is actually authorized to answer your question.
Krsna has already established himself as the appropriate person to teach the science of bhakti as described in Verse 4.1. Here, Arjuna is teaching all of us the art of questioning. He has heard Krsna out but still has a doubt and so he asks Krsna to clarify it.
This is where the subtleties of bhakti are revealed. After finding the right guide/teacher and formulating the appropriate question/s the most important thing is the attitude behind the questioning. Is it one of genuine curiosity and inquiry or one of arrogance? It's this attitude that actually determines how much knowledge is imparted from the bhakti yogi to the student.
These are three elements to perfecting the art of questioning - finding the right teacher, asking the right question and checking to see what your attitude is when asking it. Try them out and see how it works for you!