"...He doesn't necessarily do so..."???
Clearly you don't understand Romans 9:
Rom 9:9 For this [is] the word of promise, At this time will I come, and Sara shall have a son.
Rom 9:10 And not only [this]; but when Rebecca also had conceived by one, [even] by our father Isaac;
Rom 9:11
(For [the children] being not yet born, neither having done any good or evil, that the purpose of God according to election might stand, not of works, but of him that calleth
Rom 9:12 It was said unto her, The elder shall serve the younger.
Rom 9:13
As it is written, Jacob have I loved, but Esau have I hated.
Uh, this is proof positive that God most certainly chooses to do so. And here Paul affirms that in the case of Jacob and Esau!!
Rom 9:14 ¶ What shall we say then? [Is there] unrighteousness with God? God forbid.
In reality, ALL those who deny God's sovereign decrees (i.e. necessarily chooses) declare God as being "unrighteous". You have just done that, whether wittingly or NOT.
Rom 9:15 For he saith to Moses,
I will have mercy on whom I will have mercy, and I will have comp***ion on whom I will have comp***ion.
Rom 9:16 So then
[it is] not of him that willeth, nor of him that runneth, but of God that sheweth mercy.
Did you catch that?? God will have mercy on whom HE SO CHOOSES. Why? So that salvation is according to ELECTION (uh, remember Paul says that it wasn't according to their "works"?). Election is not dependent upon the one who "wills" it. It's not dependent upon one who "runs" (after it) but is SOLEY dependent upon God who "SHOWS MERCY".
Ya still wanna keep to your theology that "God doesn't necessarily so choose"??
If so, I suggest you continue to read and read Romans 9 IN CONTEXT until it sinks in.
Rom 9:17 For the scripture saith unto Pharaoh,
Even for this same purpose have I raised thee up, that I might shew my power in thee, and that my name might be declared throughout all the earth.
What did Paul just write? Uh...something about His PURPOSE in rasing up Pharaoh in order to demonstrate His power? Could you please enlighten everyone here how THIS is NOT a case of God NOT "necessarily choosing"??
Sure sounds like God necessarily CHOOSING to me. Got any legitmate "interpretation" BASED UPON THE BIBLE AND THE BIBLE ALONE?
Rom 9:18 Therefore hath he mercy on whom he will [have mercy], and
whom he will he hardeneth.
Catch that again? Paul declares that God WILL have mercy upon whom HE SO CHOOSES, and He will HARDEN those WHOM HE SO CHOOSES.
Sure ya wanna keep to your original thoughts here?
Rom 9:19 Thou wilt say then unto me, Why doth he yet find fault? For who hath resisted his will?
And here Paul anticipates the objections of those who don't like God's SOVEREIGN CHOICE IN ELECTION. Count yourself included.
Rom 9:20
Nay but, O man, who art thou that repliest against God? Shall the thing formed say to him that formed [it], Why hast thou made me thus?
Paul just asked YOU who do you think you ARE that you can reply against Him. Serious stuff, here.
Rom 9:21
Hath not the potter power over the clay, of the same lump to make one vessel unto honour, and another unto dishonour?
But you've as much as said that isn't the case here. God doesn't necessarily "choose" one to be either a "vessel unto honor" and ANOTHER UNTO DISHONOR.
Rom 9:22 [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:
Rom 9:23 And that he might make known the riches of his glory on the vessels of mercy, which he had afore prepared unto glory,
Rom 9:24 Even us, whom he hath called, not of the Jews only, but also of the Gentiles?