I thought I would jump in...
Here is something that helped me in understanding this verse:
John 6:27-29 (Amplified New Testament)
27 Stop toiling and doing and producing for the food that perishes and decomposes [in the using], but strive and work and produce rather for the [lasting] food which endures [continually] unto life eternal; the Son of Man will give (furnish) you that, for God the Father has authorized and certified Him and put His seal of endorsement upon Him.
28 They then said, What are we to do, that we may [habitually] be working the works of God? [What are we to do to carry out what God requires?]
29 Jesus replied, This is the work (service) that God asks of you: that you believe in the One Whom He has sent [that you cleave to, trust, rely on, and have faith in His Messenger].
The context is Jesus tells them to stop working for things that don't matter for the only work that God desires of them is that they believe in His Son.
This can be confirmed by looking here:
1Th 1:2-5 We give thanks to God always for all of you, constantly mentioning you in our prayers, (3) remembering before our God and Father your work of faith and labor of love and steadfastness of hope in our Lord Jesus Christ. (4) For we know, brothers loved by God, that he has chosen you, (5) because our gospel came to you not only in word, but also in power and in the Holy Spirit and with full conviction. You know what kind of men we proved to be among you for your sake.
I hope that helps.
-Nathan