The central issue in the story is the law. The expert in the law who questioned Jesus has kept the law impeccably, but what Jesus highlights is that compliance with the law cannot deliver mercy. Mercy cannot be commanded. Mercy is several steps beyond the law, and if you want to inherit eternal life (which was the lawyers original question) then one must go beyond law.
The innkeeper is promised reimbursement to the equivalent of the distance he travels beyond the law. On the evening overlooking the day the money runs out the innkeeper has a choice, will he go on caring into the following week? To do so is to live with mercy and to live in faith that the Samaritan is coming again.
This introduces a fascinating eschatological dimension to the story.
I think the challenge for the reader, individually and corporately as God’s people, is the same one the innkeeper faced. You see, the Good Samaritan is the only one in the story who acted mercifully out of his own resources. It was his donkey, his oil and wine, his money. I believe that such love is beyond us. This is why I think we are not called to love like him. We are called to love and be merciful like the innkeeper, who does it all out of the given and promised resources of the Samaritan. This is life by faith.
It is also the kind of life that is lived out in faithful obedience to a promise. The Samaritan says he is coming again and will bring payment with him. We are called to live today in the confident expectation that our Lord is returning, and he brings our reward with him. Till then we live with the resources he has left us, principally his Holy Spirit.
But it is also a life we must choose. Every day. Because every day we face a multitude of choices in which we can decide to live eschatologically, legalistically or roguishly. And goodness knows the church has done a good job of the latter two.