Truly, I say to you that whoever says to this mountain, ‘Be taken up and thrown into the sea,’ and does not doubt in his heart but believes that what he says comes to pass, it will be for him. 24 For this reason I say to you, all whatever you pray for and ask, believe that you received it, and it will be to you.
These rudimentary comments were prompted by a conversation with Andrew Jones in Amsterdam about the eschatological significance of Jesus’ saying about moving mountains as it is found in connection with the cursing of the fig tree in Jerusalem (Mk. 11:23; Matt. 21:21) and the failure of the disciples to cast out the boy’s demon following the transfiguration (Matt. 17:20).
It seems that the saying either had or came to have proverbial significance (cf. 1 Cor. 13:2 and a few rabbinic examples listed in C.A. Evans, Mark 8:27-16:20, 189).
There are important allusions to Moses in the transfiguration story - both the giving of the Law on a mountain and an echo of Deuteronomy 32:5, 20 in his complaint about a ‘faithless and perverse generation’ in Matt. 17:17. It seems unlikely that Jesus is thinking in terms of overthrowing the mountain of the Law at this point (see Matt. 5:17-18), but he may have made a link between the perverse and faithless generation of Deut. 32:20 and the burning of the foundations of the mountains in 32:22, in which case the saying would have to do with the coming judgment on a people that does not have the faith in God to cast out the evil that possesses it. But that seems a bit too much for the context - and I don’t see why that should be made the direct outcome of the disciples’ faith. So I would hesitate to attach too much significance to it here.
The Jerusalem saying is more likely to have eschatological significance though I don’t see a very strong OT antecedent. There is the general idea of making mountains level in preparation for the coming of YHWH to restore Jerusalem (cf. Is. 40:3-5; 45:2; 49:11; Pss. Sol. 11:4; Bar. 5:7); but these are mountains in the wilderness, on the way back from Babylon, not Mount Zion, which is seen as the highest of the mountains on earth (cf. Is. 2:2). Or there is the specific imagery of Zechariah 14:4, though again the imagery is rather different. (An allusion to Daniel 2:44-45 seems to me unlikely when it is here so clearly God who acts to set up the kingdom.) But the important thing to keep in mind is that both for Jesus and Paul the main point of the saying has to do with faith, not with eschatological expectation, and I rather think that this makes these OT passages less relevant.