As per Bhagavad Gita Karma yoga is the way for a human to attain salvation. In this process its not necessary to isolate oneself from this material life. A karma yogi is very much a part of this material world but his actions are performed only for the sake of performing them without thinking about the result of his actions. Because Lord Krishna says in Gita that Results are anyway in his hands and not in the hands of the performer.
Basically What I understand from this is that idea behind "karma yoga" is to destroy the "Ego" which considers itself to be the doer of acts and hence intends to take the credit, which in reality is not so.
Hence the theory "Karma yoga" needs to be applied to cut down "Ego". Krishna told Arjuna to "Do your prescribed duty but dont wait for the result". Everything under the sun moves as per the will of God but the living entity under false ego considers himself to be the doer and hence takes the credit, but he forgets that result that he got is bestowed upon him as per Gods will.
Hence to strike a balance between material and spiritualism and to adopt both for a balanced life, Lord Krishna says to become a "Karma yogi". By practice of which we can still attain salvation. It means for a Karma yogi he achieves both the worldly material pleasures but at the same time because he is free from material desires, hes not attached to them and performs his tasks correctly as per required situation to achieve success for welfare of the society