Prema means when you engage to yourself for satisfying Krsna’s senses. Why gopis are exalted? Because their only endeavor was to satisfy Krsna’s senses. Therefore Caitanya Mahaprabhu recommended, ramya kacid upasana vraja-vadhu-vargena ya kalpita. They had no other business.

From Srila Prabhupada’s lecture on Srimad-Bhagavatam 1.7.24 — September 21, 1976, Vrndavana