What is a door? It is a means of moving through a barrier or partition or a portal helping us to go from one area to another.
A wall on the other hand is a permanent barrier whether it's between two separate rooms within a building or even could be a barrier between the safety of your home and the dangers present outside of your home.
Another form of barrier is the spiritual barrier called sin that hinders our ability to be in the presence of GOD and obtain from Him all that HE offers to us. All of these and other forms of barriers need to have a means which enables us to be able to pass through them and that means is called a door.
In ( John 14:6 ) JESUS said,"I am the way, the truth, and the life: no man cometh unto the Father, but by me". So what does that mean? Also in (Matt 7:14) HE said " Because straight is the gate, and narrow is the way, which leadeth unto life, and few there be that find it ". JESUS has just said that HE is the way, then tells us that the way through HIM is a narrow way; also, that the way through the gate is a straight way. Next, HE tells us that this way leads to life, but there will be few who will actually find their way to that life.