The Bible answers both of your questions in Exodus, chapters 4-14. The answers it gives will not do?
Don't sell your answer short. There is additional scripture outside of Exodus giving the answer of
God hardened Pharaoh's heart.
Romans 9:17 For Scripture says to Pharaoh: I raised you up for this very purpose, that I might display my power in you and that my name might be proclaimed in all the earth. 18 Therefore God has mercy on whom he wants to have mercy, and
he[God] hardens whom he wants to harden.
This text contains a quote from Exodus that has already been noted in this thread. The purpose of Paul quoting is to add additional explanation on the doctrine of
God's Sovereign Choice. To this Paul says:
19 One of you will say to me: Then why does God still blame us? For
who is able to resist his will? 20 But who are you, a human being, to talk back to God? Shall what is formed say to the one who formed it, Why did you make me like this?[h] 21
Does not the potter have the right to make out of the same lump of clay some pottery for
special purposes and some for
common use?
Which contains an O.T. quote from Isaiah in two places:
Isaiah 29:16 You turn things upside down,
as if the potter were thought to be like the clay!
Shall what is formed say to the one who formed it,
You did not make me?
Can the pot say to the potter,
You know nothing?
Isaiah 45:9 Woe to those who quarrel with their Maker,
those who are nothing but potsherds
among the potsherds on the ground.
Does the clay say to the potter,
What are you making?
Does your work say,
The potter has no hands?
God need not explain his plan, but Paul does explain why God makes two different kinds of pots; one for mercy, one for destruction.
Rom 9:22 What if God, although choosing to show his wrath and make his power known, bore with great patience the objects of his wrathprepared for destruction? 23 What if he did this to
make the riches of
his glory known to the
objects of his mercy, whom he prepared in advance for glory
This is not a quote but lines up exactly with Exodus 14:4 And I will harden Pharaohs heart, and he will pursue them.
But I will gain glory for myself through Pharaoh and all his army, and
the Egyptians will know that I am the Lord. So the Israelites did this.
As if this was not enough, Paul in verses 25 through 29 quotes four more O.T. passages of God's Sovereign Choice.
To all that can not accept this clear word of God, you need to heed the warning of verse 20
But who are you, a human being, to talk back to God?