Doors, they are a physical reality and they hold many facts about life metaphorically. This proves true in Scripture.
In Matthew 6:6 we read the red words of Jesus instructing believers to use the door in order to acquire privacy for prayer. This is an important element of prayer because Jesus discourages the opposite type of prayer in the verse before (v.5) - "do not be like the hypocrites, for they love to pray standing in the synagogues and on the street corners to be seen by others." Get secluded with God.
Then in Mark 13:34, Jesus teaches for His own to be on guard and watch at the door for the return of the house owner.
Doors as barriers or obstacles are not to be feared with the Lord on your side. Jesus proved that to the resurrected body walls and closed doors were no problem as He appeared to the Disciples -"On the evening of that first day of the week, when the disciples were together, with the doors locked for fear of the Jewish leaders, Jesus came and stood among them and said, 'Peace be with you!'" (John 20:19)
However, of all the Keys the Lord Jesus possesses, the one that seems the most important - He does not forcefully use. Jesus paid for The Key to our Heart with His life, but He elects not to use it and awaits acceptance of His invitation as you hear His knock on the door of your heart and hear Him say, "Here I am! I stand at the door and knock. If anyone hears my voice and opens the door, I will come in and eat with that person, and they with me." - Revelation 3:20
God holds all the keys. He even has The Master Key for all the doors of your heart/life. He will unlock many a room inside your heart; He will open many a door in your life too - but first, you have to open up to Him, the front Door.