Mark 8:12

12 When he heard this, he sighed deeply in his spirit and said, “Why do these people keep demanding a miraculous sign? I tell you the truth, I will not give this generation any such sign.”

Mark 8:12 Meaning and Commentary

Mark 8:12

And he sighed deeply in his Spirit
In his human soul; and which shows that he had one, and was subject to grief and sorrow, and all passions and infirmities, excepting sin. This deep sigh was on account of the hardness of their hearts, the malignity of their minds, and insincerity of their intentions; who had no view to come at truth by this inquiry, but to ensnare him:

and saith, why doth this generation seek after a sign?
when so many have been shown among them, and they will not believe:

verily I say unto you, there shall no sign be given to this
generation:
such as they desired; namely, one from heaven. The Evangelist Matthew adds, "but the sign of the Prophet Jonas"; (See Gill on Matthew 16:4), (See Gill on Matthew 12:40).

Mark 8:12 In-Context

10 Immediately after this, he got into a boat with his disciples and crossed over to the region of Dalmanutha.
11 When the Pharisees heard that Jesus had arrived, they came and started to argue with him. Testing him, they demanded that he show them a miraculous sign from heaven to prove his authority.
12 When he heard this, he sighed deeply in his spirit and said, “Why do these people keep demanding a miraculous sign? I tell you the truth, I will not give this generation any such sign.”
13 So he got back into the boat and left them, and he crossed to the other side of the lake.
14 But the disciples had forgotten to bring any food. They had only one loaf of bread with them in the boat.