Jesus the propitiation

whom God set forth as a propitiation by His blood, through faith

Romans 3:25

Jesus is the propitiation.

The mercy seat at the time of the Old Testament was used to make atonement for the sins of the people, once a year the mercy seat was in the most holy place.

Then he shall kill the goat of the sin offering, which is for the people, bring its blood inside the veil, do with that blood as he did with the blood of the bull, and sprinkle it on the mercy seat and before the mercy seat.

Leviticus 16:15

Now when Moses went into the tabernacle of meeting to speak with Him, he heard the voice of One speaking to him from above the mercy seat that was on the ark of the Testimony, from between the two cherubim; thus He spoke to him.

Numbers 7:89

Moses had a personal relationship with God.

and the Lord said to Moses: Tell Aaron your brother not to come at just any time into the Holy Place inside the veil, before the mercy seat which is on the ark, lest he die; for I will appear in the cloud above the mercy seat.

Leviticus 16:2

Today we can freely enter to the presence of God, Jesus has paid the price once and for all, sacrificed Himself for the forgiveness of our sins, He has expiated our sins.
Jesus is the Lamb of God,

The Lamb of God who takes away the sin of the world

John 1:29

When Jesus died on the cross,

Then the veil of the temple was torn in two from top to bottom.

Mark 15:38

Jesus offered us the most holy place, we can approach God with confidence, not through our works, but through the grace of God manifested in Jesus Christ.

Let us enter the presence of God through Jesus Christ, put our lives in the hands of Christ and He will take care of us.

above it were the cherubim of glory overshadowing the mercy seat.[…] the priests always went into the first part of the tabernacle, performing the services. But into the second part the high priest went alone once a year, not without blood, which he offered for himself and for the people’s sins committed in ignorance; 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.
But Christ came as High Priest of the good things to come, with the greater and more perfect tabernacle not made with hands, that is, not of this creation. Not with the blood of goats and calves, but with His own blood He entered the Most Holy Place once for all, having obtained eternal redemption. For if the blood of bulls and goats and the ashes of a heifer, sprinkling the unclean, sanctifies for the purifying of the flesh, how much more shall the blood of Christ, who through the eternal Spirit offered Himself without spot to God, cleanse your conscience from dead works to serve the living God? And for this reason He is the Mediator of the new covenant, by means of death, for the redemption of the transgressions under the first covenant, that those who are called may receive the promise of the eternal inheritance.

Hebrews 9:5-15