Jesus answered them, “This is the work of God, that you believe in him whom he has sent.” — John [6:29]
The context of this verse in John is Jesus sharing that He is the bread of life. Those who were listening to Him had received sustenance and their stomachs were filled. This is interesting because after they ate and were fulfilled in their physical need, they wanted to know how they could please God and how they could do the work that God requires of them.
Jesus answered them and said that they needed to simply believe. I find it interesting that belief is the requirement to please God. Believing in Him. To have faith in, to trust and have confidence in Him.
These are truly stunning words when you think about it. All the false gods of the world require brutal acts of devotion. Only Jesus Christ requires the heart to believe. Simply believe. Have faith. Trust in Him. When you do this, you will have done the work of God.