The Lord is everywhere, in both the material and spiritual domains, and He appears for the sake of His devotees when there is friction between His devotee and the nondevotee. As electricity is generated by friction of matter anywhere and everywhere, the Lord, being all-pervading, appears because of the friction of devotees and nondevotees. When Lord Kṛṣṇa appears on a mission, all His plenary portions accompany Him. When He appeared as the son of Vasudeva, there were differences of opinion about His incarnation. Some said, "He is the Supreme Personality of Godhead." Some said, "He is an incarnation of Nārāyaṇa," and others said, "He is the incarnation of Kṣīrodakaśāyī Viṣṇu." But actually He is the original Supreme Personality of Godhead—kṛṣṇas tu bhagavān svayam (SB 1.3.28)—and Nārāyaṇa, the puruṣas and all other incarnations accompany Him to function as different parts of His pastimes. Mahad-aṁśa-yuktaḥ indicates that He is accompanied by the puruṣas, who create the mahat-tanva. It is confirmed in the Vedic hymns, mahāntaṁ vibhum ātmānam.
Lord Kṛṣṇa appeared, just like electricity, when there was friction between Kaṁsa and Vasudeva and Ugrasena. Vasudeva and Ugrasena were the Lord's devotees, and Kaṁsa, a representative of the karmīs and jñānīs, was a nondevotee. Kṛṣṇa, as He is, is compared to the sun. He first appeared from the ocean of the womb of Devakī, and gradually He satisfied the inhabitants of the places surrounding Mathurā, just as the sun enlivens the lotus flower in the morning. After gradually rising to the meridian of Dvārakā, the Lord set like the sun, placing everything in darkness, as described by Uddhava.