Rom 8:1
There is therefore now no condemnation to them which are in Christ Jesus, who walk not after the flesh, but after the Spirit.
When are believers first in Christ ? They are first in Christ before the foundation of the WorldEph 1:4 and Paul writes of believers this blessed Truth 2 Tim 1:9
9 Who hath saved us, and called us with an holy calling, not according to our works, but according to his own purpose and grace, which was given us in Christ Jesus before the world began,
In The Purpose of God [which is a reality in His Own Mind] all believers in Christ were in Him BEFORE the foundation of the World, and this by an Election Union Eph 1:4
4 According as he hath chosen us[believers] in him before the foundation of the world, that we should be holy and without blame before him in love:
God's Election gives us being in Christ, a virtual being in Him though not physically actual, much like how Levi was said, by the Purpose of God, to be in the loins of Abraham Heb 7:9-10
9 And as I may so say, Levi also, who receiveth tithes, payed tithes in Abraham.
10 For he was yet in the loins of his father, when Melchisedec met him.
This is a revelation of the Mind of God and His Purpose ! Also in the same way was all the elect in Adam !
Now this is a very critical point being made here , because without this Elective and Virtual Union in Christ and with Christ, that actually constituted the Elect in Him, Christ could not have died for their sins ! Understand 1 Cor 15:3
3 For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures;
That can only be True of those who were in Him at the time of His Death !
Without being in Him,Christ could not have died for their sins, because there would not have been no legal basis before God's Law and Justice to have imputed or charged their transgressions upon Him for Him to Justly die for them !
Thats why Paul could say as well as any other true believer this Gal 2:20
20 I am crucified with Christ: nevertheless I live; yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by the faith of the Son of God, who loved me, and gave himself for me.
In the original it reads I was or have been crucified with Christ !
It means together with in the point of time, and that could only have been by Elective and Vitual and Legal Union with Him by the Purpose of God !