Work is worship. Work is meditation. Serve all with intense love without any idea of agency and without expectation of fruits or reward. You will realise God. Service of humanity is service of God.
Work elevates when done in the right spirit without attachment or egoism. If you are a bhakta (devotee), feel you are a nimitta or instrument in the hands of God. If you adopt the path of Jnana, feel that you are a silent Sakshi (witness) and that Prakriti does everything. All work is sacred. There is no menial work from the highest view-point (from the view-point of the Absolute, from the view-point of Karma Yoga).
It is selfishness that has deplorably contracted your heart. Selfishness is the bane of human life. Selfishness clouds the understanding. Selfishness is petty-mindedness. Bhoga (sensual enjoyment) increases selfishness and selfish pravritti. It is the root cause of human sufferings. Real spiritual progress starts with selfless service.
The spirit of service must be deeply ingrained in your very bones, cells, tissues, and nerves. The reward is invaluable. Practise and feel the cosmic expansion and infinite ananda (bliss). Tall talk and idle gossiping will not do, my dear friends. Evince intense zeal and enthusiasm for work. Be fiery in the spirit of service.
A Karma Yogi does not expect even a return of love, appreciation, gratitude, or admiration from the people whom he is serving.
You must be very vigilant in scrutinising your motives during action. You must be ever introspective. By and by, when the heart becomes purer and purer through constant work, your actions will be perfectly disinterested and selfless.
In the mind there are three doshas, viz., mala (impurities like lust, wrath, greed, etc.),vikshepa (tossing of the mind), and avarana (veil of ignorance). Mala is removed through nishkamya Karma Yoga; vikshepa by means of upasana (worship); and avarana by means of study of Vedantic literature and jnana. Karma Yoga gives chitta suddhi. It purifies the heart and prepares the mind for the dawn of knowledge (jnana udaya).
Only he who has reduced his wants and controlled his indriyas [senses] can do Karma Yoga. How can a man of luxury, with his indriyas revolting, serve others? He wants everything for himself, and wants to exploit and domineer over others. Another qualification is that he must have a balanced mind. He must be free from raga-dvesha (likes and dislikes) also. “An action which is ordained, done by one who is undesirous of fruit, devoid of attachment, without love or hate—that is called pure.” Gita: Chapter XVIII-23.
You must learn the secret of renunciation or the abandonment of the fruits of action. Long is the lesson, toilsome the practice. You have to combine energy in work, with indifference to the result of the work.
Aspirants must work as energetically as the children of this world, but they must substitute a new motive; they work that the divine law may be fulfilled, that the divine purpose may be promoted, that the Will of God may be carried out in every direction. This is the new motive and it is one of the all compelling forces; they work for God alone. Thus acting they create no karma-bond for it is desire that binds.
Now, the attainment of renunciation is difficult and requires prolonged and patient practice. The probationer will begin by trying to care less about the results brought to him personally by his actions; he will try to do his very best, taking equally whatever comes. If success follows, he will check the feeling of elation; if failure, he will not permit depression to master him. Persistently he will repeat his efforts and will do his best with every duty that comes his way and will begin to show the balanced state of mind which marks the crowning strength and detachment of the soul.
Source: Practice of Karma Yoga By H.H. Sri Swami Sivananda