From the Greater to the Lesser

Paul reasons like this: since God did not spare his own Son, then sure he must and will freely give us all things with him. Why is that?
Paul is reasoning in Romans 8:32 from the hard to the easy, or from the greater to the lesser. God desired two things: not to see his Son made a mockery by sinneres; and not to see his peole denied infinite future grace. Surely it is more likely that he will spare his Son than that he will spare us. But no. He did not spare his Son.
What a truth! Giving us all things is the easy thing! Think on that every time you fear being denied something that owuld be good for you. Creating the world and running it for the good of his people is a relatively easy thing for God to do compared to handing over his Son to ridicule and torture. But he did it. Ann now all future grace is not only sure; it is easy.

Future Grace, by John Piper