The role of the Holy Spirit in salvation is well-attested in Scripture, as John Piper helpfully catalogs. He rightly says, ‘no Spirit, no Salvation’. There is however a curious little story in Acts (Acts is full of curious little stories) that jarred me a little bit when I first read it, because it seems to contradict, or at the very least complicate, the Spirits role in salvation:
‘And it happened, while Apollos was at Corinth, that Paul, having passed through the upper regions, came to Ephesus. And finding some disciples he said to them, “Did you receive the Holy Spirit when you believed?” So they said to him, “We have not so much as heard whether there is a Holy Spirit.” And he said to them, “Into what then were you baptized?” So they said, “Into John’s baptism.” Then Paul said, “John indeed baptized with a baptism of repentance, saying to the people that they should believe on Him who would come after him, that is, on Christ Jesus.” When they heard this, they were baptized in the name of the Lord Jesus. 6 And when Paul had laid hands on them, the Holy Spirit came upon them, and they spoke with tongues and prophesied. Now the men were about twelve in all.’ (Acts 19:1-7)
This is quite an interesting situation. It’s not referenced again in Scripture, and the tone doesn’t strike one as overly urgent. Paul doesn’t appear to question the disciples’ salvation, and he acknowledges that they have believed, nor does the Bible call them anything but ‘disciples’. Paul’s action isn’t to lead them to repent and believe the Gospel but to lay hands on them, whereupon the Spirit comes on them and they prophesy. The number of disciples mirrors the number of disciples at Pentecost, and both events resemble each other in that the end result of the Spirit coming upon them is tongues and prophecy.
So what’s going on here? Clearly, there can’t be salvation wholly apart from the Spirit. John Piper is correct here. However, this passage does seem to lend credence to the Pentecostal idea of a ‘second filling of the holy spirit’ or a ‘second blessing’ , often mentioned in the context of a baptism of the Holy Spirit where tongues is seen as the evidence of a second filling (this is distinct from the Wesleyan doctrine of ‘second blessing’’). This is perhaps a topic for another time, though.
At any rate, it’s clear that while there is no salvation apart from the Spirit, there appears to be a sense in which believers in Christ can be believers without even knowing that there is a Holy Spirit or without what might be called the indwelling of the Holy Spirit. It would even appear that knowledge of the Spirit isn’t necessary for the salvation of believers in the New Testament; this would make salvation even more monergistic in the sense that one can be saved and be counted a believer without any knowledge of key aspects of salvation, even continuing into the Christian life. Salvation is an act of God through and through, perhaps to an extent whether the believer knows it or not. Is there salvation apart from the Spirit? No. Does salvation require anything of us, even knowledge of the Holy Spirit, even continuing on into the disciples life? No. Salvation requires God and nothing else. God’s mighty act of salvation and continuing work of sanctification in the Christian life are contingent on God alone, and now what the believer does or doesn’t know.
Immediately preceeding Levitucs 19:18, which Jesus quotes in the parable (as you noted) is a series of injunctions of Israel’s practice of justice – treating the poor fairly, no injustice in judgement, no stealing, no swearing, fairly well-known moral teachings. These sayings/teachings/whatever have a fairly universal quality – I have a hard time seeing these commands to properly execute justice as pertaining to *only* Israelites/covenant people.
Having said that, I fully agree that the background question relates to the question of membership in the people of God. I don’t think it follows, though, that the status of ‘neighbor’ is restricted to those who are alienated (sp?) covenant members.
Following from that (my Barthianism is about to show – take that, Wright!) I think that all people are, in a sense, the people of God by virtue of God’s election of humanity in Christ. What follows from that is that while all people are elect, not all people accept said election, and hence resist (I strongly agree with Lewis when he says that hell is locked from the inside out) the grace of the covenant, and are hence alienated from the covenant. So I see there being a distinction between the people of God who are in the Messiah, and the people of God more broadly as those who are elected by God in his election of Christ. The former are charged with, as you said, restoring the alienated and wounded, who are the latter.