A door is a means of getting into somewhere or getting out of a building. There are different kind of doors – some are big, some (as in Alice in Wonderland) very small; some open in both directions (as in restaurants, allowing easy access in and out of the kitchen); some are elaborate and ornate, others are functional and plain.
Doors feature in the Bible too: from the door of prayer (see Matt 7:8) to the ‘door for effective work’ (1 Cor 16:9) to the open door placed before us by Jesus (see Rev 3:7-9).
Stephen preached on the ‘door of faith’ (Acts 14:27) last night, talking about how faith can be different sizes, just as doors can. The door (or for sci-fi fans, the portal!) is a threshold from one area to another and faith is first of all the means of our entrance into God’s kingdom. We are born again into God’s family not through our natural heritage or through circumcision, but through faith. We enter by faith through THE door, Jesus (John 10:9), for ‘if anyone enters through me, he will be saved.’
Faith, however, is also the means of God’s entrance into our hearts. God seeks to be involved in our lives, but we have to allow Him access. We can keep the door shut on Him if we want. But if we allow Him entrance, the King of glory wants to be part of our lives!
“Lift up your heads, you gates; be lifted up, you ancient doors, that the King of glory may come in. Who is this King of glory? The LORD strong and mighty, the LORD mighty in battle. Lift up your heads, you gates; lift them up, you ancient doors, that the King of glory may come in. Who is he, this King of glory? The LORD Almighty— he is the King of glory.” (Ps 24:7-10)
Faith is also the means of entrance of the Kingdom into us. If Christ comes in, He enters with gifts. The measure of the blessing that we know in our lives depends to a large extent on how wide we open the door of our hearts to allow the King of Glory to come in. 
Just as the Tardis door opens to reveal an area much bigger than would appear possible from the outside, just as a tap can be opened slightly to allow a trickle of water through or can be opened fully to allow the water to gush out, so we know the fullness of God’s blessing in our lives largely by how wide we open the door to allow Him to enter. God delights to bless His children; He has good gifts to lavish upon us. We are the ones who decide if we want to be ‘full on’ in God or not.
The Christian life is a race. The London Marathon was run on 17th April 2011… a race where we see all kinds of people participate in what is a huge test of endurance. The Christian life is like a marathon. How we finish is as important as how we start, and we need to understand that the door of faith is important throughout our lives, for faith is an essential ingredient in pleasing God and in unlocking His blessings in our lives.