Believe is not a soft verb

When they found Him on the other side of the sea, they said to Him, "Rabbi, when did You get here?" Jesus answered them and said, "Truly, truly, I say to you, you seek Me, not because you saw signs, but because you ate of the loaves and were filled. Do not work for the food which perishes, but for the food which endures to eternal life, which the Son of Man will give to you, for on Him the Father, God, has set His seal." Therefore they said to Him, "What shall we do, so that we may work the works of God?" Jesus answered and said to them, "This is the work of God, that you believe in Him whom He has sent." (John 6:25-29 NASB)

        How can believing be any kind of work? Isn't belief a rather abstract affirmation of some claim, idea or concept? Usually, perhaps, but Jesus had a more concrete meaning here. Referring to Mark 11:22-24, where Jesus spoke of faith in God, after he told them faith, without doubt, could move a mountain into the sea, he spoke of more practical faith-matters, specifically, "all things for which you pray and ask." Then comes the key word "believe," but not "that you will receive them." Jesus said, "that you have received them," stating that God knew the need and granted it before it was voiced.
        That speaks of far more than a passive, abstract affirmation of something. It speaks of stepping on an invisible bridge in full confidence that it is really there—because God clearly and understandably said to do it. Then, knowing that even if it wasn't there, the falling would somehow glorify God.
        People throughout history have done outrageous things because they felt that God had commanded it: cruel, murderous things. Yes, under the Old Covenant, some of those commands were really from God, because the greater work that God wanted accomplished required it. Today, the only "Promised Land" tells us to possess is the life characterized by God's unique holiness and love, without which no one will see Him.