The doorway with the blood on the door frame, each side and over top, represents the old Passover. It represents the law, the covering of sin, and the passing of judgment based on the required sacrifice...A spotless innocent lamb.
Jesus also represents the doorway. He is the doorway to the Father. The spotless lamb of God. He is the blood poured out for the sins of mankind. That those who would simply believe, and take His covering upon them, would have their sins forgiven. And His judgment would pass over them on the day of His return.
He came not to abolish the law...He came to fulfill it. And He gave us with the new Passover...a new commandment.
“A new commandment I give you: Love one another. As I have loved you, so you must love one another. By this, everyone will know that you are my disciples, if you love one another.” John 12:34-35