I post these apparently redundant verses to suggest that the Author of Scripture seems to intend a point be made.....
KJV Matthew 12
38Then certain of the scribes and of the Pharisees answered, saying, Master, we would see a sign from thee.
39But he answered and said unto them, An evil and adulterous generation seeketh after a sign; and there shall no sign be given to it, but the sign of the prophet Jonas:
40For as Jonas was three days and three nights in the whale's belly; so shall the Son of man be three days and three nights in the heart of the earth.
KJV Matthew 16
1The Pharisees also with the Sadducees came, and tempting desired him that he would shew them a sign from heaven.
2He answered and said unto them, When it is evening, ye say, It will be fair weather: for the sky is red.
3And in the morning, It will be foul weather to day: for the sky is red and lowering. O ye hypocrites, ye can discern the face of the sky; but can ye not discern the signs of the times?
4A wicked and adulterous generation seeketh after a sign; and there shall no sign be given unto it, but the sign of the prophet Jonas. And he left them, and departed.
KJV Mark 8
11And the Pharisees came forth, and began to question with him, seeking of him a sign from heaven, tempting him.
12And he sighed deeply in his spirit, and saith, Why doth this generation seek after a sign? verily I say unto you, There shall no sign be given unto this generation.
KJV Luke 11
29And when the people were gathered thick together, he began to say, This is an evil generation: they seek a sign; and there shall no sign be given it, but the sign of Jonas the prophet.
30For as Jonas was a sign unto the Ninevites, so shall also the Son of man be to this generation.
And then this makes a good summation of the point...
KJV 1 Corinthians 1
18For the preaching of the cross is to them that perish foolishness; but unto us which are saved it is the power of God.
19For it is written, I will destroy the wisdom of the wise, and will bring to nothing the understanding of the prudent.
20Where is the wise? where is the scribe? where is the disputer of this world? hath not God made foolish the wisdom of this world?
21For after that in the wisdom of God the world by wisdom knew not God, it pleased God by the foolishness of preaching to save them that believe.
22For the Jews require a sign, and the Greeks seek after wisdom:
23But we preach Christ crucified, unto the Jews a stumblingblock, and unto the Greeks foolishness;
24But unto them which are called, both Jews and Greeks, Christ the power of God, and the wisdom of God.
25Because the foolishness of God is wiser than men; and the weakness of God is stronger than men.
26For ye see your calling, brethren, how that not many wise men after the flesh, not many mighty, not many noble, are called:
27But God hath chosen the foolish things of the world to confound the wise; and God hath chosen the weak things of the world to confound the things which are mighty;
28And base things of the world, and things which are despised, hath God chosen, yea, and things which are not, to bring to nought things that are:
29That no flesh should glory in his presence.