CC Ādi 4.15-16
rāga-mārga bhakti loke karite pracāraṇa
ei dui hetu haite icchāra udgama
During the period of Lord Kṛṣṇa’s appearance, the killing of asuras or nonbelievers such as Kaṁsa and Jarāsandha was done by Viṣṇu, who was within the person of Śrī Kṛṣṇa. Such apparent killing by Lord Śrī Kṛṣṇa took place as a matter of course and was an incidental activity for Him. But the real purpose of Lord Kṛṣṇa’s appearance was to stage a dramatic performance of His transcendental pastimes at Vrajabhūmi, thus exhibiting the highest limit of transcendental mellow in the exchanges of reciprocal love between the living entity and the Supreme Lord. These reciprocal exchanges of mellows are called rāga-bhakti, or devotional service to the Lord in transcendental rapture. Lord Śrī Kṛṣṇa wants to make known to all the conditioned souls that He is more attracted by rāga-bhakti than vidhi-bhakti, or devotional service under scheduled regulations. It is said in the Vedas (Taittirīya Up. 2.7), raso vai saḥ: the Absolute Truth is the reservoir for all kinds of reciprocal exchanges of loving sentiments. He is also causelessly merciful, and He wants to bestow upon us this privilege of rāga-bhakti. Thus He appeared by His own internal energy. He was not forced to appear by any extraneous force.