Therefore they said to Him, "What shall we do, so that we may work the works of God?"(John 6:28)
When I understood and believed that Jesus, being the Son of God, died for my sins so that I might have life in heaven I asked this question too. I was eager to please and was quickly given an answer: read your Bible, pray, tell others this good news about Jesus, be nice to everyone, go to church every Sunday, find a ministry in the church. Just to name a few.
I tried that for about eleven years. At the end of ten years I was not as sure that Jesus was good news and at the end of the eleventh year I KNEW He was not good news. He had promised me joy and left me with guilt, promised acceptance and provided condemnation, promised peace and left me with torment that I could never do everything that He asked. I was angry, betrayed, and told God that He was a liar and a fraud.
I told Him I was not going to try any more. I could not sleep that night (yes, I could only stay that angry for most of one night.) I was between a rock and hard place. I could not go on as I had been, but I could not get rid of God either. In my very deepest being, in spite of the evidence, I knew that He was my only answer. That is when I realized that "I will never leave you nor forsake you." wasn't just a gushy, feel-good promise but somewhat of a threat.
There was a purpose for all my striving and trying to work the works of God. It was to come to the absolute certainty that only God can work the works of God. After I had initially believed Jesus, that He was the Son of God as He said He was, I accepted what other people told me that Jesus wanted of me. When I was fully burnt out, I was ready to be refocused on Jesus Himself and what He said He required of me, and not what others told me about Him.
Jesus answered and said to them, "This is the work of God, that you believe in Him whom He has sent." (John 6:29) Now here is the "light burden and easy yoke" that I was promised. At first sight He says that our work is to believe Him. But, when you look closer He calls even that the work of God.
Is this too simplistic? Is this passivity? I really would like to know what you think. I think that it would be ridiculous for God to require something of us that we cannot do. Jesus plainly stated, "I can do nothing on My own. . ."(John 5:30) If He could do nothing on His own what do you think that we can do? My conclusion is that God both wills and works His good pleasure in an unexplainable mystery.