‘And the Pharisees came forth and began to question with him, seeking of him a sign from heaven, tempting him.'
On His arrival the Pharisees came and began to dispute with Him. How genuine they were we do not know. Probably their aim was simply to discredit Him. But it brings out how, in spite of all that He has done and achieved they are still as blind as ever. So they point out that if He really is the Coming One they must have some spectacular sign from Him, something which will be blindingly convincing, and be an outward and compelling proof of divine authority in accordance with their own thinking.
Perhaps they sought the ‘bath kol', that distant voice from heaven, speaking so that they could hear, or fire coming down on the enemies of Israel as it had for Elijah and Elisha. But in fact no sign would have convinced them of the truth, for they did not want someone like Jesus. They wanted something that would confirm them in their own position. And even then they would have interpreted it in their own fashion.
There is a deliberate contrast here. Mark, as he will emphasise shortly (Mark 8:18-21), wants us to realise that such a sign had been given, to those who had eyes to see and ears to hear, in the feeding of the seeking crowd but that it was not available to the doubting Pharisees who only had their own leaven (corrupted bread) to make do with. For God does not win people by signs. That is not their purpose (and indeed if it were they would fail). They are rather given in order to boost those who are already genuinely seeking and to those who believe (as with John the Baptiser in prison - Matthew 11:2-6).
‘Tempting Him.' They were putting Him to the test, but it was a repeat of the old temptations at the beginning, the temptation to take the easy and spectacular way out.