Mark 8:12

12 But sighing deeply in His spirit, He said, "Why does this generation demand a sign? I assure you: No sign will be given to this generation!"

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 and immediately got into the boat with His disciples and went to the district of Dalmanutha.
11 The Pharisees came out and began to argue with Him, demanding of Him a sign from heaven to test Him.
12 But sighing deeply in His spirit, He said, "Why does this generation demand a sign? I assure you: No sign will be given to this generation!"
13 Then He left them, got on board [the boat] again, and went to the other side.
14 They had forgotten to take bread and had only one loaf with them in the boat.