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 [Hebrews 9:7]
The “second part” in the above verse refers to the holy of holies. It was the innermost room in the tabernacle or temple where the ark of covenant was placed. There was a mercy seat on the ark of covenant. God spoke to Moses and His people from above the mercy seat (see Exodus 25:17-22). Thus the ark of covenant symbolizes the presence of God. And as shown in the above verse, in those days only the high priest could enter the holy of holies and stand before God.
Therefore, brethren, having boldness to enter the Holiest by the blood of Jesus [Hebrews 10:19]
Now, by the blood of Jesus believers of Jesus can enter the holy of holies and stand before God because the blood of Jesus, which was shed for us on the cross, serves as the blood necessary for atonement (notice that in the first verse of this post, Hebrews 9:7, the high priest could not enter the holy of holies without blood). Note, it is impossible for a person to stand before God on his own. In other words, we have access to God through Jesus, and only through Jesus.
There are 3 other verses in the bible that also support this.
Therefore, having been justified by faith, we have peace with God through our Lord Jesus Christ, through whom also we have access by faith into this grace in which we stand, and rejoice in hope of the glory of God. [Romans 5:1-2]
For through Him we both have access by one Spirit to the Father. [Ephesians 2:18]
according to the eternal purpose which He accomplished in Christ Jesus our Lord, in whom we have boldness and access with confidence through faith in Him. [Ephesians 3:11-12]