Work is worship means working for God. Work for God is called karma yoga.
Karma means actions, and yoga means to connect. So karma-yoga is the process of connecting with God, through your actions.
Srila Prabhupada says:
When you add this word yoga, that means bhakti. Yoga means bhakti. Somebody is addicted to these material activities. So they are advised to act in the terms of karma-yoga. What is that karma-yoga? The karma-yoga is described in the Bhagavad-gita as yat karosi.
“Whatever you are doing, kurusva tad mad-arpanam. You are working? All right. What you have earned?” “
One thousand dollars.” “Give Me.” Are you prepared? Krishna is asking, kurusva tad mad-arpanam. So if anyone is agreed, “Yes, Krishna, here is the money for You,” then he’s a karma-yogi.
Otherwise he’s a karmi. And the difference between karma-yogi and karmi means he has to suffer the result, good or bad, and karma-yogi has nothing to suffer, because he’s doing everything for Krishna.
Just like Arjuna. In the beginning he considered that “If I kill my kinsmen and my grandfather I’ll be sinful.”
Yes. But the same thing he acted under the direction of Krishna. Krishna wanted. So he’s free. So karma-yogi means he is free from the reaction of activities. He is karma-yogi.
Similarly jnana-yogi. Somebody is addicted to work very hard. Somebody is addicted to speculate philosophically. So for the speculator, Krishna says, bahunam janmanam ante jnanavan mam prapadyate [Bhagavad Gita 7.19].
The persons who are addicted to speculative knowledge, after many, many births, he comes to the understanding: vasudevah sarvam iti [Bg. 7.19], “Vasudeva, Krsna, is everything.”
That means termination of knowledge. That is jnana-yoga. If by his research work he tries to understand what is Krishna by philosophy or by science or anything, by chemistry, by physics… That is recommended in the Srimad-Bhagavatam:
atah pumbhir dvija-srestha / varnasrama-vibhagasah
svanusthitasya dharmasya / samsiddhir hari-tosanam
Svanusthitasya dharmasya samsiddhir hari-tosanam. It doesn’t matter in whatever activities you are engaged, but if you want to know whether your engagement is leading to perfection, then this is the test of perfection.
What is that test of perfection? Samsiddhir hari-tosanam [SB 1.2.13]. Whether by your work the Supreme Personality of Godhead is satisfied.
Just like Arjuna did. Arjuna, in the beginning, he wanted to satisfy himself by not fighting, and he fought to satisfy Krishna. That is perfection. Samsiddhir hari-tosanam [SB 1.2.13]. Yes.
—Lecture on Bhagavad-gita 4.1 — Montreal, August 24, 1968