Salvation is a CONDITIONAL free gift from God. No one receives God’s free gift of salvation unconditionally.
What Would Jesus Do? or Say???
25 When they found him on the other side of the lake, they asked him, “Rabbi, when did you get here?”
26 Jesus answered, “Very truly I tell you, you are looking for me, not because you saw the signs I performed but because you ate the loaves and had your fill. 27 Do not work for food that spoils, but for food that endures to eternal life, which the Son of Man will give you. For on him God the Father has placed his seal of approval.”
28 Then they asked him, “What must we do to do the works God requires?”
29 Jesus answered, “The work of God is this: to believe in the one he has sent.”
30 So they asked him, “What sign then will you give that we may see it and believe you? What will you do? 31 Our ancestors ate the manna in the wilderness; as it is written: ‘He gave them bread from heaven to eat.’[c]”
32 Jesus said to them, “Very truly I tell you, it is not Moses who has given you the bread from heaven, but it is my Father who gives you the true bread from heaven. 33 For the bread of God is the bread that comes down from heaven and gives life to the world.”
34 “Sir,” they said, “always give us this bread.”
35 Then Jesus declared, “I am the bread of life. Whoever comes to me will never go hungry, and whoever believes in me will never be thirsty. 36 But as I told you, you have seen me and still you do not believe. 37 All those the Father gives me will come to me, and whoever comes to me I will never drive away. 38 For I have come down from heaven not to do my will but to do the will of him who sent me. 39 And this is the will of him who sent me, that I shall lose none of all those he has given me, but raise them up at the last day. 40 For my Father’s will is that everyone who looks to the Son and believes in him shall have eternal life, and I will raise them up at the last day.”
In Jn 6:27 Jesus clearly said to WORK for the meat that endures unto everlasting life that the Son of man shall GIVE you.
—Jesus settles the issue in saying one must WORK for everlasting life. Not just any kind of work but an obedient work in doing His will. In this text belief is said to be a work, a work given to those people to do. As you point out the people asked “what must DO”. Jesus did not tell them do nothing else you attempt to earn everlasting life but instead Jesus gave them a work to do, the work of believing. Belief is not just a mental assent of the mind but is an action, it is what one does.
Secondly the verse says Jesus “GIVES” everlasting life, it is a gift Jesus freely GIVES. Since Jesus freely gives everlasting life then why in the world did He say to WORK for it??? Because the gift of everlasting life is ==CONDITIONAL== therefore one must work to meet the conditions Christ has put upon this free gift and in this context belief is a condition one must work in order to receive this free gift Christ gives.
From other verses we find repentance Lk 13:3, confession Mt 10:23-33 and baptism Mk 16:16 are also conditions Christ has places upon His free gift. This is why the unbeliever will not receive Christ’s free gift of everlasting life. The impenitent will not receive the free gift of everlasting life. Those that refuse to confess Christ or be baptized will not receive this free gift that Christ gives.