The passage
      v1. Paul sees his apostolic ministry as a calling, as a binding request from God. God's will in the matter certainly covers the initial calling, but also covers his apostolic ministry. This then is his authority, something the trouble-makers in the church do not possess. As for the mention of Sosthenes, we don't know much about him. He is probably not an apostle, but could be the Sosthenes of Acts 18:17. Obviously, he was assisting Paul and was accorded the title "brother".
      v2a. Paul addresses his letter to the "church of God in Corinth". The word "church" (assembly) can refer to the local congregation, or to the universal heavenly assembly of all believers. Here it is used of the local assembly. Paul describes this group as "sanctified in Christ Jesus". We know well that Christ's death and resurrection gained our forgiveness and therefore God's approval. Yet, it does more than this. Through a personal association with Christ we actually become God's holy (set apart, separated) children. In the Son of God we become sons of God. Not only are we justified in Christ, we are also sanctified in him. This idea is reinforced in the phrase "called to be holy", or literally "called and holy". When we put our trust in Jesus we became one of God's called out people, his chosen people, the people he has separated from the world to himself, the "holy" ones of God (holy persons, saints - those set apart for the service of God). Of course, just because we are "holy" before God, doesn't mean we can deny our present corruption. It is because of our present state of sin that the scriptures constantly urge us to be what we are.
      v2b. This phrase is grammatically difficult. It is most likely an introduction to v3: "to you believers at Corinth and to all believers everywhere (literally - in every meeting-place) who call on the name of the Lord Jesus... grace and peace to you..." Paul here reminds us how we become one of the called out (holy) people of God; we called out to Jesus, we put our trust in him.
      v3. Paul concludes the address with a blessing of "grace and peace". A Gentile would say "grace" ("greeting to you") and a Jew would say "peace", but Paul says both. "Grace" is the free and unmerited offer of God's favour to believers in Christ. "Peace" is the outcome of God's favour - well-being in the circle of God's friendship. So, when we offer "grace and peace" to a brother, we are praying that they may know the full extent of God's favour and experience it more day-by-day.

Peace be with you
      In liturgical churches which follow a "catholic" form, such as Anglican or Lutheran, there is a little greeting given during the service where the minister says "the peace of the Lord be always with you". In some churches there is a time of personal greeting to those next to us. Each says "peace be with you." In our passage for study Paul gives his readers an ancient greeting that goes way back to Old Testament times.
      Greetings often become ritualized and devoid of power. "Good morning", which means "God be with you this morning", is an example. Yet, "peace" is still a very substantial greeting. The Jews, of course, still use it. They say " shalom", which means "peace be with you." Paul the apostle added the word "grace", grace being the substance of God's favour, and "peace" its outcome.
      So then, if we were to greet each other with the word "peace", using these first few verses from Paul's letter to the Corinthians as a guide to it's meaning, we would end up with a very substantial greeting indeed. In the second verse Paul identifies something of the weight of God's grace:
        i] We are "church". We gather in particular places to address Jesus and be addressed by Jesus. Jesus' promise is that where two or three gather in his name he will be present with us. What wonderful favour God shows us, what wonderful grace, in that he would even bother to meet with such a motley crew. Peace is ours when the Lord meets with us.
        ii] We are "called". We have the privilege of standing as one of God's "peculiar" people. We actually have the right to see ourselves as specially loved by God. This, of course, is none of our own doing; Jesus has done it all for us. We get into this chosen group by asking, seeking, knocking; we cry out for mercy and it is given. Such grace, such peace.
        iii] We are "sanctified", made "holy". Religious people, yes even church going Christians, often think holiness (purity and perfection in the sight of God) is shaped in their lives by striving to obey the law. Yet, God's favour extends even to the gift of holiness. Through our relationship with Christ we possess, as a gift, the righteousness of Christ. Grace indeed, and what wonderful peace is ours in such grace.

v2
      th/ ekklhsia/ "to the church" - to the assembly. "To the gathered believers."
      tou qeou "of God" - Probably a genitive of possession, belonging to God. A reminder that the church does not belong to the minister etc. "To God's church in Corinth", CEV.
      hJgiasmenoiV (aJgiazw) perf. pas. part. dat. "to those sanctified" - to ones having been sanctified. Participle as a substantive. The word carries the Old Testament sacrificial sense of that which is set apart to God for a special use. The use of the perfect underlines a past act with present ramifications. An epexegetical phrase, further explaining the sense of "church". "To those Christ has made holy", Phillips.
      en "in [Christ Jesus]" - in, on. Possibly "by", ie. instrumental rather than a locative sense, although "in", as in "union with", is more like Paul.
      klhtoiV aJgioiV "called to be holy" - called saints/holy. It is unlikely that Paul has an ethical sense in mind here. We are not called/invited to be good, but rather to stand approved in God's sight through our union with Christ, "called to be God's men and women", Phillips.
      sun + dat. "together with ...." - with. It is probably "the church of God in Corinth, together with ....."
      toiV epikaloumenoiV (epikalew) pres. part. "those [everywhere] who call on" - the ones calling upon, invoking. Participle as a substantive. The present tense indicates a durative (repeated, ongoing) approach to the divine. An allusion to Joel 3:5. The sense is of worship, "invoke the name of the Lord", Moffatt.
      en panti topw/ "everywhere" - in every place. The phrase is used in extant literature of a synagogue and therefore Paul is probably specifically referring to the meeting place of believers.
      autwn kai hJmwn "their Lord and ours" - theirs and ours. Grammatically, "their place and ours", as in "meeting place", follows the order of the Greek sentence, but the antecedent "Lord Jesus Christ" makes more sense, so NIV.