I would think people being saved and trusting God is beyond man's ability, but God is able to place His promise in there hearts.
I'm not sure that predestination is exactly cut and dry though because even the elect could be deceived if possible and also the the verse concerning the grafted in branches being plucked off as well as the seed on rocky soil. It is clear that it isn't by man's goodness whatsoever that anyone can enter heaven.
This verse below children of the promise seems to imply children who receive the promise. Seed that has been given the life of God.
Romans 9:8 That is, They which are the children of the flesh, these are not the children of God: but the children of the promise are counted for the seed.
Romans 9:21 Hath not the potter power over the clay, of the same lump to make one vessel unto honour, and another unto dishonour?
22 What if God, willing to shew his wrath, and to make his power known, endured with much longsuffering the vessels of wrath fitted to destruction:
23 And that he might make known the riches of his glory on the vessels of mercy, which he had afore prepared unto glory,