Gopi is a prime pillar of Bhagavad Gita rather Bhagavad Puran. Without Gopis I believe Krishna would not have been able to teach us the lesson of devotion, love, oneness with God, salvation (भक्ति सायुज्य प्रेम मोक्ष).
The relationship of Gopi and Krishna is interesting. The more I study it, the more I read it I realize that through the example of Gopis, Krishna wanted to show us, being busy in cores of day-to-day life you can attain nearness of Krishna…if your efforts are strong and you have confidence you can get oneness with Krishna.
Some scripts says Gopis were saints performing meditations since ages to attain nearness with Krishna. These saints took birth as Gopis to live with Krishna.
They taught us a good way to be near with Krishna.
1. Chanting – While working in home, doing day-to-day activities like cooking, cleaning, etc they chant the name of Krishna and sign his glory.
2. Work offered to Krishna – Though they use to cook for their family and work for their family members the center of all their work were Krishna. While cooking they use to think what Krishna would like to eat. Krishna is center of their attention.
3. Longing for Krishna – While Krishna was away in forest with cows they use to be eagerly waiting for him to return. When he would return they stand out in the entrance of their house with smile on their face welcoming Krishna.
4. Forgoing every barrier – For Krishna they forgo barrier of their family and went to meet Krishna, they forgo barrier and came out of river to take clothes.