In plain words
If you carry out all karmas not as an offering to tṛṣṇā but as an offering to Kṛṣṇa, that itself turns into Bhakti.
Pure Prema set upon an object that is lovely, of another kind, and most excellent is itself Bhakti. Most excellent means that which does not change: that is the sense. Prema too is just so; it must stay unchanging through time, place and circumstance. In the Gītā this is called samacitta. Pairs of opposites such as heat and cold, joy and sorrow, blame and praise do not move that Prema in the least. Yogaḥ karmasu kauśalaṃ, He said. Whether karma yoga, Bhakti yoga or Jñāna yoga, each achieves oneness through karmas and reaches the fulfilment of its fruit in gaining these: the ending of sorrow and the gaining of Ānanda.
Look closely at the way a tree grows. First the trunk; then the branches and twigs; then the flowers; then the green fruit and the ripe fruit; just so, for these trees of life karma itself is the trunk; Bhakti itself is the branches and twigs and the blossoms that spread their fragrance; Jñāna itself is the fruit and the sweetness within it. Karma or Bhakti without the fruit of Jñāna are mere laughable doings. Jñāna without karma and Bhakti, too, is nothing but dry Vedānta!
On the path called Bhakti there are two kinds, saguṇa Bhakti and nirguṇa Bhakti. In the feeling that oneself is one and the Paramātma another, people take up many kinds of worship and try to earn the Grace of that Paramātma. This is one way. To merge one's own individuality in the Paramātma, to experience directly the oneness, the Divinity and the Saccidānanda in all beings, and to rejoice in it: that is nirguṇa Bhakti. Some people sell children all kinds of dolls made of sugar; in the town they stand at the school gate and sell them. Each child longs for one shape or another, gives money, takes it home and is delighted. In the same way the saguṇa bhakta worships his chosen deity with form, as the One with attributes; the other, who honours the sugar that shines in all the dolls, dwells on that oneness alone, rejoices and is rid of sorrow, is the nirguṇa bhakta. There is no difference in the sugar; the delusion that there are differences arises from form and name, that is all.
In Bhāratīya culture yajñas and yāgas have an important place. When yajñas are performed, a rite called Soma-pā has to be done; there are many rules and procedures for it, and restrictions too. You must grasp its inner meaning well. Soma means the moon. Pā means drinking! How can anyone drink the moon? You need not be bewildered, thinking, “This does not fit, does it?” Because the moon means “Manas”, whose presiding deity is the moon itself. “Candramā manaso jātaḥ”: the moon and Manas are closely related. Drinking the moon means restraining Manas, which roams about at will, and conquering it yourself: that alone is the inner meaning; whoever controls Manas can become worthy of yajñas and yāgas. If you perform karmas without control of Manas, they are only fruitless karmas!