Nroug7: A door to a house is vital, however, if one does not build stairs then the door is pointless. In order for the door to be useful, stairs must follow.
I was thinking for a while over this and...
a) "a door to a house is vital" - yes, every house needs an entrance - in other case it is just "a box": you can be inside but can not go out, or in. Also, an entrance needs a door for safety - you can select who can go in or out.
b) "stairs must follow" - well, weird word, "follow" - can be understood as "after" - "after door" - but stairs after door? in house? rather not. I think this "stairs must follow" means "stairs must be next thing to build", and not really "after door" nor "inside house" - I think stairs are "outside". If they "must be" it means our house is somewhere high or low - I think rather "high", because if "low" then you can still jump in without stairs.
So, what we have here: "I" am at "house" which is somewhere "high", it has some "door" and "stairs" are leading down.
In reality - it could be house on the tree, mountain, it can be also mentioned lighthouse. But it all can be too easy rather too guess? So it needs to be some other meaning. As one of others "door" can represent some "point to aim". A way to it can be hard and leading up so that way is called "stairs". To reach "the door", we need to know where is it first. Then we can go in this direction "by stairs".