26 Jesus answered them and said, Verily, verily, I say unto you, Ye seek me, not because ye saw the miracles, but because ye did eat of the loaves, and were filled.
27 Labour not for the meat which perisheth, but for that meat which endureth unto everlasting life, which the Son of man shall give unto you: for him hath God the Father sealed.
30 They said therefore unto him, What sign shewest thou then, that we may see, and believe thee? what dost thou work?
31 Our fathers did eat manna in the desert; as it is written, He gave them bread from heaven to eat.
32 Then Jesus said unto them, Verily, verily, I say unto you, Moses gave you not that bread from heaven; but my Father giveth you the true bread from heaven.
33 For the bread of God is he which cometh down from heaven, and giveth life unto the world.
34 Then said they unto him, Lord, evermore give us this bread.
35 And Jesus said unto them, I am the bread of life: he that cometh to me shall never hunger; and he that believeth on me shall never thirst.
36 But I said unto you, That ye also have seen me, and believe not.
49 Your fathers did eat manna in the wilderness, and are dead.
50 This is the bread which cometh down from heaven, that a man may eat thereof, and not die.
Abdu'l-Baha:
...Therefore, miracles are not a proof. For if they are proofs for those who are present, they fail as proofs to those who are absent.
...But in the day of the Manifestation the people with insight see that all the conditions of the Manifestation are miracles, for They are superior to all others, and this alone is an absolute miracle. Recollect that Christ, solitary and alone, without a helper or protector, without armies and legions, and under the greatest oppression, uplifted the standard of God before all the people of the world, and withstood them, and finally conquered all, although outwardly He was crucified. Now this is a veritable miracle which can never be denied. There is no need of any other proof of the truth of Christ.
The outward miracles have no importance for the people of Reality. If a blind man receives sight, for example, he will finally again become sightless, for he will die and be deprived of all his senses and powers. Therefore, causing the blind man to see is comparatively of little importance, for this faculty of sight will at last disappear. If the body of a dead person be resuscitated, of what use is it since the body will die again? But it is important to give perception and eternal life - that is, the spiritual and divine life.
The meaning is not that the Manifestations are unable to perform miracles, for They have all power. But for Them inner sight, spiritual healing and eternal life are the valuable and important things.