John 6 (KJV)
29 Jesus answered and said unto them, This is the work of God, that ye believe on him whom he hath sent.
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.
37 All that the Father giveth me shall come to me; and him that cometh to me I will in no wise cast out.



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"4. Yet again, God is unchanging in his promises. Ah! we love to speak about the sweet promises of God; but if we could ever suppose that one of them could be changed, we would not talk anything more about them. If I thought that the notes of the bank of England could not be cashed next week, I should decline to take them; and if I thought that God's promises would never be fulfilled—if I thought that God would see it right to alter some word in his promises—farewell Scriptures! I want immutable things: and I find that I have immutable promises when I turn to the Bible: for, "by two immutable things in which it is impossible for God to lie," he hath signed, confirmed, and sealed every promise of his. The gospel is not "yea and nay," it is not promising today, and denying tomorrow; but the gospel is "yea, yea," to the glory of God.
Believer! there was a delightful promise which you had yesterday; and this morning when you turned to the Bible the promise was not sweet. Do you know why? Do you think the promise had changed? Ah, no! You changed; that is where the matter lies. You had been eating some of the grapes of Sodom, and your mouth was thereby put out of taste, and you could not detect the sweetness. But there was the same honey there, depend upon it, the same preciousness. "Oh!" says one child of God, "I had built my house firmly once upon some stable promises; there came a wind, and I said, O Lord, I am cast down and I shall be lost." Oh! the promises were not cast down; the foundations were not removed; it was your little "wood, hay, stubble" hut, that you had been building. It was that which fell down. You have been shaken on the rock, not the rock under you. But let me tell you what is the best way of living in the world.
I have heard that a gentleman said to a Negro, "I can't think how it is you are always so happy in the Lord and I am often downcast." "Why Massa," said he, "I throw myself flat down on the promise—there I lie; you stand on the promise—you have a little to do with it, and down you go when the wind comes, and then you cry, 'Oh! I am down;' whereas I go flat on the promise at once, and that is why I fear no fall."
Then let us always say, "Lord there is the promise; it is thy business to fulfill it." Down I go on the promise flat! no standing up for me. That is where you should go—prostrate on the promise; and remember, every promise is a rock, an unchanging thing. Therefore, at his feet cast yourself, and rest there forever."

Source: A Sermon (No. 1)
Delivered on Sabbath Morning, January 7th, 1855, by the REV. C. H. Spurgeon At New Park Street Chapel, Southwark.
"I am the Lord, I change not; therefore ye sons of Jacob are not consumed."—Malachi 3:6