There are two ways of constantly thinking of Krishna – as a devotee and as an enemy.

“In Bhagavad-gita (4.10) the Lord says:

vita-raga-bhaya-krodha man-maya mam upasritah
bahavo jnana-tapasa puta mad-bhavam agatah

“Being freed from attachment, fear and anger, being fully absorbed in Me and taking refuge in Me, many, many persons in the past became purified by knowledge of Me–and thus they all attained transcendental love for Me.”” There are two ways of constantly thinking of Krishna–as a devotee and as an enemy. A devotee, of course, by his knowledge and tapasya, becomes free from fear and anger and becomes a pure devotee. Similarly, an enemy, although thinking of Krishna inimically, thinks of Him constantly and also becomes purified. This is confirmed elsewhere in Bhagavad-gita (9.30), where the Lord says:

api cet su-duracaro bhajate mam ananya-bhak
sadhur eva sa mantavyah samyag vyavasito hi sah

“Even if one commits the most abominable actions, if he engages in devotional service he is to be considered saintly because he is properly situated.” A devotee undoubtedly worships the Lord with rapt attention. Similarly, if an enemy (suduracarah) always thinks of Krishna, he also becomes a purified devotee. The example given here concerns the grassworm that becomes beelike because of constantly thinking of the bee that forces it to enter a hole. By always thinking of the bee in fear, the grassworm starts to become a bee. This is a practical example. Lord Krishna appears within this material world for two purposes–paritranaya sadhunam vinasaya ca duskrtam: to protect the devotees and annihilate the demons. The sadhus and devotees certainly think of the Lord always, but duskrtis, the demons like Kamsa and Sisupala, also think of Krishna in terms of killing Him. By thinking of Krishna, both the demons and devotees attain liberation from the clutches of material maya.”

Source: A.C. Bhaktivedanta Swami Prabhupada (2014 edition), “Srimad Bhagavatam”, Seventh Canto, Chapter 01 – Text 29