Winman, election is unconditional. That means not based on anything that man may or may not do. God chooses those whom He will. What is that to you or me? That is strictly the prerogative of God. Do you read well Winman, God chooses those whom He will and what is that to you or me? That is strictly the prerogative of God.
Where do the scriptures say election is unconditional? That is a man-made doctrine, you cannot find that in scripture. Yes, God can choose whosoever he likes, whether it is conditional or not.
And Scripture tells us:
Romans 8:29, 30
29. For whom he did foreknow, he also did predestinate to be conformed to the image of his Son, that he might be the firstborn among many brethren.
30. Moreover whom he did predestinate, them he also called: and whom he called, them he also justified: and whom he justified, them he also glorified.
The Scripture states God, Winman, not I, not you, God!
Now Winman, foreknow does not mean that God knew who would believe. It is obvious that God knows all things and that includes those who believe and those who will not. So saying that God knows who is going to believe and chooses or elects them on that basis is foolish. That makes God subject to the whims of sinful man!
It does not, it makes God sovereign. If God determines the condition, then God is in control.
That is why I showed Judges 7, God told Gideon that whom he picked (God), they should fight with Gideon. In this case God chose the 300 men who lapped water like a dog.
Jud 7:4 And the LORD said unto Gideon, The people are yet too many; bring them down unto the water, and I will try them for thee there: and it shall be, that of whom I say unto thee, This shall go with thee, the same shall go with thee; and of whomsoever I say unto thee, This shall not go with thee, the same shall not go.
Gideon did not choose the 300, God did.
Now as to your story. The reason God whittled the number of men from 10,000 to 300 has nothing to do with the way they got a drink from the creek. God reduced the number of men so they could not boast: I did it! I did it. I whupped the Midianites but these other 299 helped a little. Rather they had to give God the Glory.
The same is true of the Doctrines of Sovereign Grace and those who believe the Doctrines of Grace, they give all Glory to God.
You are correct that God chose only 300 so Israel could not boast. And the scriptures say God has chosen the poor who are rich in faith. He has chosen the foolish and despised to confound the wise and mighty.
1 Cor 1:27 But God hath chosen the foolish things of the world to confound the wise; and God hath chosen the weak things of the world to confound the things which are mighty;
28 And base things of the world, and things which are despised, hath God chosen, yea, and things which are not, to bring to nought things that are:
29 That no flesh should glory in his presence.
Jam 2:5 Hearken, my beloved brethren, Hath not God chosen the poor of this world rich in faith, and heirs of the kingdom which he hath promised to them that love him?
God has chosen the poor because generally speaking the poor are rich in faith. They look to God as their refuge, this is shown over and over in scriptures. God does this to confound the wise and mighty who trust in their riches or own wisdom.
Nowhere do the scriptures say election is unconditional, it doesn't even make sense. God doesn't choose people randomly. We are directly told in scripture who God chooses and why.