Then why do you believe the day of atonement was yet future?
The final 3 feasts fulfilled in 70ad, supposedly...
In the OC, the High Priest would enter the Holy of Holies and place the blood on the mercy seat. However, the atonement wasn't complete until the High Priest came back out and pronounced the atonement as being finished.
After the cross Christ Jesus entered the Most Holy of Holies in heaven, and placed His blood on the mercy seat for ALL sins for all time.
The salvation wasn't fully completed (finished) until He returned in 70AD.
The writer of Hebrews tells us that:
(Heb 9:28) so Christ was sacrificed once to take away the sins of many; and he will appear a second time, not to bear sin, but to bring salvation to those who are waiting for him.
Paul said the same thing:
(Eph 1:13-14 )... When you believed, you were marked in him with a seal, the promised Holy Spirit, 14 who is a deposit guaranteeing our inheritance until the redemption of those who are God’s possession...
And here:
(2 Cor 1:22) set his seal of ownership on us, and put his Spirit in our hearts as a deposit, guaranteeing what is to come.
And here:
(Rom 13:11) And do this, understanding the present time: The hour has already come for you to wake up from your slumber, because our salvation is nearer now than when we first believed.
Paul was a Pharisee, he understood the duties of the High Priest for the Day of Atonement.
Paul knew the atonement would be complete when Jesus returned.