We only speak in this way because in conditional life we take it that everything has a beginning; however, in the absolute or spiritual life there is neither beginning nor end. Yet in order to understand that Rādhā and Kṛṣṇa are one and that They also become divided, the question "When?" automatically comes to mind. When Kṛṣṇa desired to enjoy His pleasure potency, He manifested Himself in the separate form of Rādhārāṇī, and when He wanted to understand Himself through the agency of Rādhā, He united with Rādhārāṇī, and that unification is called Lord Caitanya.
Why did Kṛṣṇa assume the form of Caitanya Mahāprabhu? It is explained that Kṛṣṇa desired to know the glory of Rādhā's love. "Why is She so much in love with Me?" Kṛṣṇa asked. "What is My special qualification that attracts Her so? And what is the actual way in which She loves Me?" It seems strange that Kṛṣṇa, as the Supreme, should be attracted by anyone's love.