The simplicity of the concept presented in these verses must be stated first, so that it is not lost, complicated, confused or combined with other information during study or teaching.
Here is the religion of the Lord in its simplest and purist form: To believe God is to be in right standing with God.
This principle goes back to Genesis when, “Abram believed the LORD, and he credited it to him as righteousness. “(Genesis 15:6) This verse is quoted by Paul in Romans 4:3 and Galatians 3:6 and by James in James 2:23. James sums up his quote from Genesis 15:6 this way:
" ‘Abraham believed God, and it was credited to him as righteousness,’ and he was called God's friend.” – James 2:23
Trusting God is the doorway to God. Believing the Lord’s promise is fellowship with God. In John 6: 28, 29 when the people ask, “What must we do to do the works God requires?” Jesus answers, “The work of God is this: to believe in the one he has sent.”
Earlier in John 6 Jesus had fed 5,000 Jews by multiplying bread and fish. The next day the people looked for and found Jesus on the other side of the Sea of Galilee. But, they did not understand nor did they ask for the meaning of the sign. They assumed he was the Prophet who was to come in fulfillment of Moses’ words in Deuteronomy 18:15 and (according to John 6:14-15) they wanted to make Jesus king. The Jews must have figured that with a king who could multiply food and heal the sick like Jesus did they could have the world’s best welfare/health care program once the Romans were defeated!
In response to this attitude Jesus said something to this effect, “You are looking for me, not because you understood the meaning of the sign of me multiplying bread. I gave you natural food for your natural life. And, so you are looking for me because you want breakfast, too. You simply want more natural food. Instead, you should be asking, “What kind of man is he?” Because, I am the bread of life.”
The people still did not understand the meaning of the sign of the multiplied bread and asked Jesus, “What must we do to do the works God requires?” To this Jesus replied, “The work of God is this: to believe in the one he has sent.”
Jesus was showing them that just like the natural bread fed their natural life, He was the source of eternal life. It is easy to know how to partake of natural bread – we simply take a bite, chew and swallow. Jesus was saying that partaking of spiritual bread for spiritual life is also easy – we simply believe that God has sent his son. The work of natural life is to swallow bread. The work of spiritual life is to believe God’s word.