How does spiritual knowledge free us from misery, as the Bhagavad-gita promises?

Answer summary: By first showing us the pathway to freedom from misery and then enabling us to move along that pathway.

Answer:

Suppose we have no conception of light due to having lived lifelong in a dark tunnel. Because of the darkness, whenever we move about, we experience bumps, stumbles, falls, bruises and fractures. However, because we are in darkness about darkness, that is, we don’t know that there is any alternative to darkness, we assume that such mishaps are unavoidable while moving.

In our present material existence, we are as if trapped in a maze of dark tunnels. The darkness here is due to the absence of spiritual knowledge. In the darkness of ignorance, we struggle to decide what to do and where to go in life. We make choices, but they rebound on us with undesirable consequences, leaving us dismayed and disheartened. However, over time we tend to accept such frustrations as unavoidable in life because everyone around us is also spiritually ignorant like us. Thus we stay in darkness about our darkness.

The Bhagavad-gita (04.17) illumines our way with the light of knowledge, revealing that essentially three pathways beckon us. One way takes us into the still darker areas of the tunnel where greater misery awaits us. This is the path of vikarma, the path of ignorant and immoral action. If we tread this path, we only increase our miseries the karmic reactions to our actions befall us sooner or later.

A better path is the path of karma, the path of scriptural duty and morality. Though this path takes us towards better lit areas, it still keeps us within the tunnel. We are souls, who belong to the eternal spiritual world. However, as long as we love temporary material things – even if that love be within the precincts of morality, we stay bound to material existence.

The best path is the path of akarma, the path of action that brings no karmic reactions – the path of devotional service. Devotional service redirects our love from matter to Krishna. Though we may struggle on this path too, we can take heart from the knowledge that we will soon reach the arena of light that is forever free from all struggles. When we thus act according to our spiritual nature as souls by loving Krishna, we become increasingly illumined by both the awakening of our latent spiritual wisdom and by Krishna’s enlightening grace. Thus, we march straight out of the dark tunnel to the supreme light of the eternal spiritual world.

That’s why the Bhagavad-gita urges us to choose this path of light when it assures (04.16) us that those guided by its knowledge become free from all inauspiciousness and misery.

Thus Gita wisdom first removes our darkness about darkness by informing us about the light of spiritual knowledge and then removes our darkness by taking us to the light of the spiritual world.