All or Some?

We begin reading the epistle to the Ephesians and will spend several days on it. In this epistle, we find a more mature Paul. His advice is less brunt and more refined, more palatable.
Blessed be the God and Father of our Lord Jesus Christ, who has blessed us in Christ with every spiritual blessing in the heavenly places,
even as he chose us in him before the foundation of the world, that we should be holy and blameless before him.
He destined us in love to be his sons through Jesus Christ, according to the purpose of his will,
to the praise of his glorious grace which he freely bestowed on us in the Beloved (Ephesians 1:3-5).
Paul began this epistle with a blessing to God. Then he told us that God had chosen us before the foundation of the world.  He wanted us to be holy and blameless (Ephesians 1:4). Naturally, you will ask how many are chosen, who are chosen. This is a mystery which even Paul could not answer. Diplomatically, he evaded the question by saying that God made us His sons through Jesus Christ, according to the purpose of His will κατὰ τὴν εὐδοκίαν τοῦ θελήματος αὐτοῦ. Then what is "the purpose of His will"? Why not simply say "His will"? Then that would be easier to figure out, to understand. No matter what, we still have to run for our own life. In other epistles, St Paul talks about life like running races, about prizes and about our returning to God.
As we read on, we have the impression that God would choose only some people to be His children, to be saved. He had destined only some people to receive enough grace to offset the influence of evil. When they die, they have finished their race and would receive the prizes from God.
Ethically speaking, "choosing a few" seems to be a better course of action. If everybody wins a prize in a race, there is no motivation to struggle, to lead a meaningful life. If everybody can enter heaven, there is no motivation to struggle, to sanctify our life. Therefore, it is rational for God to choose only a few, to destine them to be the Son of God.
But when we read further, we find a verse which suggests otherwise.
... a plan for the fulness of time, to unite all things in him, things in heaven and things on earth (Ephesians 1:10).
In Christ, God had a plan. God wants to unite all things in Christ. This suggests that God has chosen us all, to adopt us as His sons through Christ. God is merciful. He is able to accommodate all sinners. Of course, for the completeness of philosophical arguments, "choosing a few" is the best, the most logic argument. There are less loopholes to block. Yet, we are not dealing with logical positivism here. We are dealing with a mysterious God who reigns beyond logic. Therefore, we are able to glimpse a thin slice of hope in the above verse. God will accept all sinners at the end of the world. He has destined all souls to be saved.

My dear Advocate, such is Your kindness, I thank You. Such is Your wisdom, I am intoxicated by You. May we continue to contemplate Your mystery and attain our salvation. Amen.