Prabhupada mentions in his purport to Bg 17.3 that “It should be understood that if one’s heart is in the mode of goodness his faith is also in the mode of goodness. If his heart is in the mode of passion, his faith is also in the mode of passion. And if his heart is in the mode of darkness, illusion, his faith is also thus contaminated.”
Krsna Consciousness is by definition transcendental, and thus free from the influence of the three modes. It’s not easy for a person influenced by passion and ignorance to immediately go to a transcendental platform, therefore the mode of material goodness works as a bridge between these different stages. Only in the mode of goodness can we properly understand the process of devotional service and practice it. As long as we are conditioned by the modes of passion and ignorance our understanding and actions will be covered by these lower modes and it will be difficult to do so.
On Bg 14.17, Krsna explains that “From the mode of goodness, real knowledge develops; from the mode of passion, greed develops; and from the mode of ignorance develop foolishness, madness and illusion.” The three modes of material nature are called gunas in Sanskrit, a word that means “rope”. Just like ropes, these three modes force us to act in certain ways. Once one comes into the grip of a certain combination of the modes, it’s very hard to resist its influence. The best we can do is to reduce the influence of passion and ignorance and increase the influence of goodness by developing habits, activities, and thoughts that are conducive to it. That’s why through the Bhagavad-Gita Krsna gives us so many examples connected with the three modes, so we can understand the path to take.
At the same time, it’s important to keep in mind that the mode of goodness is still not sufficient to gain release from this material world, much less to achieve pure love of Godhead. In the Bhagavad-Gita (14.6) it’s mentioned that “sukha-saṅgena badhnāti jñāna-saṅgena”, indicating that those situated in the mode of goodness become conditioned by a sense of happiness and knowledge. On 14.9 it is mentioned that sattvaṁ sukhe sañjayati, “the mode of goodness conditions one to happiness”, and on 14.14 it’s mentioned that “When one dies in the mode of goodness, he attains to the pure higher planets of the great sages.” On 14.6 Krsna explains, by defining the mode of Godness as “nirmalatvāt” (purer than the others), but not as “pure”. All of this indicates that the mode of Godness is still material and one needs to further purify oneself to attain the transcendental platform.
How to approach this transcendental platform? Ultimately we need to learn it from people who are on such a platform, or in other words, by associating with pure devotees. One acquires some preliminary faith by hearing from devotees, and this faith brings one to accepting a self-realized spiritual master and being trained under his guidance. By spiritual practice and cultivation of transcendental knowledge one develops faith, and when this faith matures the fruit of love of Godhead manifests.
As Prabhupada mentions (17.28): “In the conditional state, people are attracted to worshiping demigods, ghosts, or Yakṣas like Kuvera. The mode of goodness is better than the modes of passion and ignorance, but one who takes directly to Kṛṣṇa consciousness is transcendental to all three modes of material nature. Although there is a process of gradual elevation, if one, by the association of pure devotees, takes directly to Kṛṣṇa consciousness, that is the best way.”