Lord Kapila was very satisfied by the request of His glorious mother because she was thinking not only in terms of her personal salvation but in terms of all the fallen conditioned souls. The Lord is always compassionate towards the fallen souls of this material world, and therefore He comes Himself or sends His confidential servants to deliver them. Since He is perpetually compassionate towards them, if some of His devotees also become compassionate towards them, He is very pleased with the devotees. In Bhagavad-gītā it is clearly stated that persons who are trying to elevate the condition of the fallen souls by preaching the conclusion of Bhagavad-gītā — namely, full surrender unto the Personality of Godhead — are very dear to Him. Thus when the Lord saw that His beloved mother was very compassionate towards the fallen souls, He was pleased, and He also became compassionate towards her.