The early church recognized "the Lord's Day" as being distinctive (Rev. 1:10). It was on the first day of the week that Christ arose victoriously from the grave and was to be observed regularly by His church.
Christians gather at other times, but it's incumbent that we gather on the first day of the week for worship (Acts 20:7). Meeting on other days for gospel meetings, classes, etc., cannot replace the Lord's Day. Since this was their common practice, Paul taught the Corinthians that it was a convenient time to contribute toward the needs of the Jerusalem church (1 Cor. 16:1-4).
We question why Christ's resurrection on the first day of the week has stamped so indelibly Sunday as the Christian's day of worship. Consider the following related events: (1) It was not originally called "Sunday", but was referred to as the "first day" of the week.
It was this day that Jesus arose from the dead becoming the Lord of both the living and the dead (Rom. 14:9).
(2) The first day was when Jesus met with His disciples. He appeared to Mary, the disciples and those on the road to Emmaus (Jn. 20:1, 11-23 Lk. 24:1, 13-15). It was on the Lord's day (Sunday), a week later, that Jesus appeared to Thomas and the disciples (Jn. 20:26). (3) Since Jesus' death and resurrection delivered us from the power of sin and death (1 Cor. 15:20-23; Rom. 5:10, 17; 8:11), Sunday is the Christian's day of celebration of deliverance and salvation. (4) The events of Pentecost in Acts 2 occurred on a Sunday. Thus, the church's birthday, the coming of the Holy Spirit, the first gospel sermon, the conversion of 3,000 and the start of Christian worship all took place on a Sunday. This being the case, it should never be reduced to a "having to attend" event, but considered an honor and privilege to observe. The Sabbath day is not the same day because the first day followed the Sabbath (Mt. 28:1).
What about Sunday evening? An injunction has been given to the elders to "feed the flock" (Acts 20:28). If they determine it important that we be present to be fed on Sunday evening, it is as vital that we be present as Sunday morning. If we do not, we become insubordinate to God's designated overseers (Heb. 13:17).