N.T. Wright says that the story Jesus tells is instead about Israel. He writes:
Consider: here is a son who goes off in disgrace into a far country and then comes back, only to find the welcome challenged by another son who has stayed put. The overtones are so strong that we surely cannot ignore them. This is the story of Israel, in particular of exile and restoration. It corresponds more or less exactly to the narrative grammar which underlies the exilic prophets, and the books of Ezra and Nehemiah, and a good deal of subsequent Jewish literature, and which must therefore be seen as formative for second-Temple Judaism. The exodus itself is the ultimate backdrop: Israel goes off into a pagan country, becomes a slave, and then is brought back to her own land. But exile and restoration is the main theme. That is what the parable is about.
Babylon had taken the people into captivity; Babylon fell, and the people returned. But in Jesus’ day many, if not most, Jews regarded the exile as still continuing. The people had returned in a geographical sense, but the great prophecies of restoration had not yet come true. What was Israel to do? Why, to repent of the sin which had driven her into exile, and to return to YHWH with all her heart. Who would stand in her way, to prevent her return? The mixed multitude, not least the Samaritans, who had remained in the land while the people were in exile. But Israel would return, humbled and redeemed: sins would be forgiven, the covenant renewed, the Temple rebuilt, and the dead raised. What her god had done for her in the exodus – always the crucial backdrop for Jewish expectation – he would at last do again, even more gloriously. YHWH would finally become king, and would do for Israel, in covenant love, what the prophets had foretold.
The Lutheran “faith vs. works” interpretation of this parable presented by many clergy is not what Jesus was driving at. As Wright puts it:
His (Jesus) welcome to all and sundry, that free commensality of which Crossan writes so movingly, was a sign that resurrection – forgiveness – restoration – return from exile – the reign of YHWH – were all happening under the noses of the elder brothers, the self-appointed stay-at-home guardians of the father’s house. The covenant was being renewed, and Jesus’ welcome to the outcasts was a vital part of that renewal.