A weapon in the tent is of no use to a warrior in the fight
When warriors are fighting a war, their most important possession is their weapon. Without it, even if they fight heroically, they will be felled by armed enemies. Additionally, even if they have a powerful weapon, if it is not with them when they are attacked, they will be defeated.
When we start practicing spiritual life, we become warriors waging war against the forces of illusion. These forces attack us with worldly desires that are like nooses. When these nooses fall on us, that is, when desires captivate us, they drag us down from principled living to immoral indulgences. Though worldly temptations promise lots of enjoyment, what they actually deliver is a drop of pleasure followed by an ocean of trouble. Only when we see with philosophical perceptiveness can we understand how worldly desires are captivating and conning us. Pertinently, the Bhagavad-gita (04.42) urges us to arm ourselves with the sword of spiritual knowledge. Being thus equipped, we see the deceptiveness of worldly allurements. And, more importantly, we see the supreme attractiveness of the ultimate spiritual reality, Krishna, thereby feeling inspired to become fixed in devotional service to him.
To be adequately armed, we need to regularly study books of spiritual knowledge such as the Gita. However, if this knowledge stays only in our books or notes, not in our head and heart, it is like a weapon in the tent – it offers us no protection when the noose of desire falls on us. Despite our best intentions and resolutions, we end up deluded and degraded.
To protect ourselves, we need to study spiritual knowledge earnestly and internalize it industriously. Once we are properly equipped, we can firmly resist temptation and persevere in bhakti-yoga practice till we become purified, thereby attaining joyful absorption in Krishna.