An Argument for the Resurrection's Importance

Preamble

I will present an argument that we can gain insight into the importance of Jesus' resurrection for the early church by the mere fact that the early Christians chose Sunday as their special day of celebration.  This is significant for evangelicals since we tend to think of Jesus' crucifixion as the Christ event par excellence.  However, it wasn't Friday that early Christians honored as we would expect if we adhered to the evangelical emphasis.

New Testament Evidence

In Revelation 1:10 there is mention of the "Lord's Day".  This probably refers to Sunday.  Since it refers to "the Lord" it is meant to recall events in Jesus' life, that is, the resurrection.  It's true that we are not told that this was Sunday or the first day of the week, but one would probably expect the author to have mentioned the "Sabbath" if that was the day.  Later Christian writings are explicit on this point (see below).

In Corinthians 16:1-2, Paul mentions the first day of the week as a time when he would gather the individual's contributions.  Paul mentions the Galatian churches in this regard so at least something is special about Sunday.  It's likely that this was the day Christian met which would make Paul's task of collection easier.

Acts 20:7 is also put forward int his regard.  Here, we are told that on the first day of the week (see Mt. 28:1; Lk. 24:1) the Christians met and broke bread.  There are references to a meal Jesus had with his followers after his resurrection (presumably on a Sunday) which use language associated with the Eucharist: Luke 24:, 30, 35 (breaking bread); 24:43 (taking the fish); John 20:19-29 and 21:13 (taking and giving bread. fish also); see Mark 16:14 and Acts 10:41.  It could be argued that the Eucharist practice was instituted by Jesus in these episodes and that is why the church does it Sunday and not Thursday as we would expect from the Last Supper.

Other Evidence

 Here is a list of some of the key reference to Sunday and its association with the resurrection of Jesus.

•  Didache 14.1 "on the Lord's Day we meet and break bread."
• Ignatuis of Antioch, Letter to the Magnesian Christians 9.1 "no longer observing the Sabbath, but living in the observance of the Lord's Day, on which our life arose through him and his death." Also from this letter: "let every friend of Christ keep the Lord's day as a festival, the resurrection-day, the queen and chief of all days." 
• Melito of Sardis wrote a treatise titled Concerning the Lord's Day
• Chrysostom, Psalms 119 "it was called the Lord's day because the Lord rose on that day."
• Eusebius, Ecclesiastical History, III, 27 Referring to a group of Ebionites who "celebrate the Lord's days very much like us in commemoration of his resurrection."  It has been argued that the Ebionites (a Jewish Christian sect) would not have observed Sunday in this way if the custom had originated outside of Palestine, which is further evidence of its antiquity.
• Epistle of Barnabas, 15.9 "we joyfully celebrate the eighth day, on which Jesus rose from the dead and, after being disclosed to us, ascended into the heavens." [see Lk. 24:51]
• Justin Martyr, Apology 1.67 Christians meet together on Sunday because "it is the first day, on which God...created the world, and the same day on which Jesus rose from the dead."
• Pliny the Younger, Book 10, letter 96 mentions that the Christians meet regularly before dawn on a fixed day.

It would be difficult to imagine a change from the Jewish Sabbath (see Col. 2:16) without a really good alternative.  The resurrection of Jesus provides such an alternative, which argues for its importance in the early church.

Theological Upshot

The resurrection of Jesus was of utmost importance to the early church.  Good Friday was good, but Easter Sunday is better!  We Christians worship on Sunday and not Friday, which is a clue to the importance of the resurrection!