“There are two kinds of devotees, known as sakama and akama. Pure devotees are akama, whereas devotees in the upper planetary systems, such as the demigods, are called sakama because they still want to enjoy material opulence. Because of their pious activities, the sakama devotees are promoted to the higher planetary systems, but at heart they still desire to lord it over the material resources. The sakama devotees are sometimes disturbed by the demons and Raksasas, but the Lord is so kind that He always saves them by appearing as an incarnation. The Lord’s incarnations are so powerful that Lord Vamanadeva covered the entire universe with two steps and therefore had no place for His third step. The Lord is called Trivikrama because He showed His strength by delivering the entire universe with merely three steps.
The difference between sakama and akama devotees is that when sakama devotees, like the demigods, fall into difficulty, they approach the Supreme Personality of Godhead for relief, whereas akama devotees, even in the greatest danger, never disturb the Lord for material benefits. Even if an akama devotee is suffering, he thinks this is due to his past impious activities and agrees to suffer the consequences. He never disturbs the Lord. Sakama devotees immediately pray to the Lord as soon as they are in difficulty, but they are regarded as pious because they consider themselves fully dependent on the mercy of the Lord. As stated in Srimad-Bhagavatam (10.14.8):
tat te ‘nukampam susamiksamano bhunjana evatma-krtam vipakam
hrd-vag-vapurbhir vidadhan namas te jiveta yo mukti-pade sa daya-bhak
Even while suffering in the midst of difficulties, devotees simply offer their prayers and service more enthusiastically. In this way they become firmly fixed in devotional service and eligible to return home, back to Godhead, without a doubt. Sakama devotees, of course, achieve from the Lord the results they desire from their prayers, but they do not immediately become fit to return to Godhead. It is to be noted herein that Lord Vishnu, in His various incarnations, is always the protector of His devotees. Srila Madhvacarya says: vividham bhava-patratvat sarve visnor vibhutayah. Krishna is the original Personality of Godhead (Krishnas tu bhagavan svayam). All the other incarnations proceed from Lord Vishnu.
Source: A.C. Bhaktivedanta Swami Prabhupada (2014 edition), “Srimad Bhagavatam”, Sixth Canto, Chapter 09 – Text 40