The way I see it:
In this age, God is raising up a nation of priests, those who will be priests in the next age and ages to come, priests after the order of Melchizedek, based not on a bloodline, nor the will of man, but based on an indestructible life.
This is why he tells us, .he who believes has everlasting life.
Now we see that this priesthood has been chosen in Christ before the commencement of the ages, to be revealed during the lifetime of each one chosen.
Chosen, kept secret [mystery], hidden in Christ until the appointed time when it will be manifested. Some of this group will be blinded [the Jews] until the rest [Gentiles] are brought in.
So we see:
44 Again, the kingdom of heaven is like unto treasure hid in a field; the which when a man hath found, he hideth, and for joy thereof goeth and selleth all that he hath, and buyeth that field. Mat 13
We are that treasure hidden in the field of the world. The work on the cross was done for us, and it was so huge that the whole world is saved in the process. Calvin got it half right. He forgot that, in paying the price for us, God bought the whole field.
God loves the whole world,
But you are a chosen generation, a royal priesthood, an holy nation, a peculiar people; that you should show forth the praises of him who has called you out of darkness into his marvelous light;
--1 Peter 2:9
"a chosen" generation
From G1586; select; by implication favorite: - chosen, elect.