Heb 9:8-10 the Holy Spirit indicating this, that the way into the Holiest of All was not yet made manifest while the first tabernacle was still standing. It was symbolic for the present time in which both gifts and sacrifices are offered which cannot make him who performed the service perfect in regard to the conscience concerned only with foods and drinks, various washings, and fleshly ordinances imposed until the time of reformation.
If it was unknown how people could stand perfectly justified in the presence of God, it was a mystery. The ceremonial law divided Jews from gentiles, and Jews from God. However, neither could enter the most Holy place, except the priest once a year, and not without blood.
How can this dividing barrier be broken down to where Jews and gentiles can enter the most Holy place (heaven), fully justified, and sanctified by a way other than animal sacrifices?
A mystery revealed by the gospel of Jesus Christ. To enter the Spiritual sanctuary, you must be born of the Spirit. But before the Spirit can enter, it must be first cleansed by the blood of Christ.
And so the mystery is, we are the temple of God, and he dwells in us.