I was asked this question recently:
I was reading John 6:28-29 & wanted to get your opinion. The people wanted to perform miracles, but Jesus said that God only wanted them to believe. If someone rebuts modern-day prophesy w/this scripture, what should I say?
I responded as follows:
The context for this statement is the feeding of the 5000. The next day the crowd figures out where Jesus has gone [across the lake] and they follow Him there. Jesus tells them that the only reason they have looked for Him is to get food. In fact, He mildly rebukes them because they did not recognize or respond to His miraculous signs, probably the miraculous feeding of the 5000 [vs.26]. Jesus tells them not to work [or pursue Him] for temporary things like food but for food that lasts [eternal life.]
Then they ask Him what is the work that God requires? In other words, “how do we measure up to God and obtain eternal life?”
Jesus says the only way to do that is through belief in Him. Faith in Jesus is, of course, the only way to God. This would have been a very scandalous thing for Him to say to the Pharisees who see their righteousness in the keeping of the traditions of the Elders [the Talmud.]
In terms of rebutting the suggestion that Jesus is not interested in our coming to faith in him as a response to his signs and wonders, we need to consider the text in both John 10:38 and John 14:11 which He says, and I paraphrase, “if you don’t believe me as a result of my words, at least believe because of the miracles I do.”
I think the passage you have brought up is actually a passage in support of belief in Jesus as the Son of God/Messiah being the result of experiencing his signs and wonders. The larger context for this verse is the history of conversions found in the Gospel of John leading up to this passage.
If you look carefully at the first 7 chapters of the book of John you will see that every conversion happens through a supernatural spiritual gift [usually the gift of prophecy or some revelatory gift]. It is a very good exercise to go through these chapters and look closely at how all the conversions take place.