The mature intellect brings forth devotion that is always in awe of creation. When something is unfathomable, the intellect is in awe. When the mind takes rest in the vastness of consciousness, only then can it know the Truth. This can only happen through Shraddha. Shraddha is not just faith, it is to love something that is beyond the purview of knowing. And if one is willing to look beyond what is already known, then the vast wealth of knowledge embraces them.
The mind keeps wandering from one sense to another in search of satisfaction. It is only when you realize that this joy is caused by something greater, you can be centered. There is a saying that when one appreciates a flower, the flower feels sad as the creator of the flower is not being appreciated. In Bhagvad Gita, Lord Krishna declares himself as the cause of all the joy of the senses. The intellect keeps getting stuck in the senses but when the mind, intellect and Chitta get fixed on the Divine, the highest can be attained.
If one is unable to be completely fixated on the Divine, then one can establish devotion through sadhana or spiritual practices. However, any practice has to be done continuously without exception and with respect. Mental tiredness gives rise to the inability to do any practice. Many people do either only Sadhana or only Seva, and Lord Krishna does not spare either. He says, 'If you work for Me then you will not be tired, this is for sure!'
Lord Krishna treats Arjuna as a friend and gives him options saying, 'If you cant even maintain your practice, then at least be part of Me. Feel total oneness with Me.' The body, mind and emotions are a result of karma. Good and bad things will happen, but be detached. 'Take refuge in My connection with you and don't ever question this relationship.'