.. but Krishna needed, but one thing from him for good to prevail. His faith and belief.
Excuse me. That is how a theist would look at it. However, my reading of BhagawadGita is different. What the later Vaishnavas made Gita into is not what it started with. Please remember, Prabhupada's translation is heavily biased in favor of his sect's views. He puts in words which are not their in the verse. Krishna's advice was to a dithering soldier, who was being influenced by relationships (family, teacher). Krishna asked Arjuna to abandon all emotions and engage in what his duty demanded. That is the most important message and purpose of BhagawadGita. The same rule can be applied in every thing in life - 'Don't be influenced by anything whatsoever, but continue to perform your duty for its own sake'.
2.14 : O son of Kuntī, the nonpermanent appearance of happiness and distress, and their disappearance in due course, are like the appearance and disappearance of winter and summer seasons. They arise from sense perception, O scion of Bharata, and one must learn to tolerate them without being disturbed.
2.15 : O best among men (Arjuna), the person who is not disturbed by happiness and distress and is steady in both is considered eligible for liberation.
2.38 : Thereafter fight for the sake of fighting, without considering happiness or distress, loss or gain, victory or defeat – and by so doing you shall never incur sin.
2.41 : The resolute have only one aim, O beloved child of the Kurus, the intelligence of those who are irresolute is many-branched.
2.47 : Your right extends to performance of your duty, but not to the fruits of your action. Never consider yourself the cause of the results of your actions, and never be enamored of inaction.
2.48 : Perform your duty equipoised, O Arjuna, abandoning all attachment to success or failure. That is known as the yoga of equanimity.