Last two verses from previous chapter are having the purpose to sow the seeds for this twelfth chapter titled bhakti-yoga. Bhakti-yoga is not another means for moksa pursuit, but it is the core for entire range of spiritual pursuit. We need to keep in mind that to own up limitless nature of oneself, only self-knowledge is the means, and ātma-jñānam is impossible without bhakti.
The word bhakti is derived from the root bhaj in the sense of service - dedicates action to Īśvara who is in the form of order of dharma. We all know that we need to do our actions in keeping with dharma, then can we say we have bhakti for Īśvara? But are we really doing dharmic action as the means for the sake of Īśvara as the end? Or are we seeing Īśvara as the means with the help of dharmic action to reach any ends which we desire like wealth, health, heaven etc? In this case this is bhakti towards oneself, not towards Īśvara. But when bhakti is the core for the entire spiritual pursuit, means it can expand from self-bhakti to Īśvara-bhakti. This is the essence of entire Veda, pathing the journey of a human being, starting one's life from karma-kanda (the initial portion of Veda) to jñāna-kanda (vedānta) to be free now and here. Let us see these stages of spiritual pursuit: 1. karma-laksana-bhakti, devotion in the form of karma - doing actions for fulfilling one's own desire but in keeping with dharma (sakāmaka-karma). Here one should look upon any result of action as prasāda - blessing from Īśvara. After certain fulfilment is there, one started to enquire if all these material benefits really can fully satisfy one's desire. And from the teaching of Veda itself one comes to know that only ātmā-jñānam can give moksa, then one starts to do karma only for purity of the mind, prepare oneself for ātma-jñānam (niskāmaka-karma). Now the purpose of karma is to become a devotee of Īśvara, not devotee of one-self. Even though in the process of following dharma in one's life, one nicely manages one's like and dislike, but this is not enough to be qualified for ātmā-jñānam. One should have certain focus and inward looking mind to stay with the subject matter. Therefore next step is:
2. upāsana-laksana-bhakti, devotion in the form of meditation. There are two kinds, one is meditation upon Īśvara with certain form (eka-rūpa-īśvara-dhyanam) and meditation upon Īśvara in all forms (aneka/visva-rūpa-īśvara-dhyanam). Both of them meditate upon Īśvara with form. Then when one understands fully the teaching of Vedānta, next step is:
3. jñāna-laksana-bhakti, contemplate on I am that nirguna-brahman.
This chapter opens with Arjuna's question which lies on the conflict of the mind whether bhakti in the form of meditation toward Īśvara with form is better or meditation towards Īśvara without form is better. Since he just saw the cosmic form of the Lord and get overwhelmed, he might think that greatness is the closest way for moksa, but he also heard how Lord Krsna praised a jñāna-yogī as the one who is not separated from him. Therefore he asked:
arjuna uvāca evam satatayuktā ye bhaktāstvām paryupāsate | ye cāpyaksaramavyaktam tesām ke yogavittamāh ||12.1|| Arjuna said In this manner, (there are) those devotees who, abidingly committed, meditate upon you and also (there are) those who seek you as one who is not subject to decline and not available for objectification. Who among them are the greatest knowers of yoga?