Since many of us don't know the distinguishing characteristics of a biblical disciple, an apostle, or the Twelve, we probably won't understand the meaning of today's first reading.
In the Christian Scriptures, a disciple is anyone - man or woman - who follows Jesus. Luke, in Acts, even employs the feminine of the Greek word. An apostle is a disciple sent out on a specific mission. Paul of Tarsus often refers to himself as an apostle. The Twelve are unique. They seem to be the twelve men (probably apostles) whom the historical Jesus chose to accompany him during his itinerant preaching ministry.
Any Jew, hearing the number 12, automatically thinks of the twelve tribes of Israel. Every one of them belongs to one of those tribes. Originally the twelve were the twelve sons of Jacob, some of the patriarchs who gave us Judaism. Scholars believe Jesus employed the Twelve as an outward sign of his conviction that the reform he was preaching applied equally to all Jews, not just those who belonged to the two prestigious tribes of his day and age - Judah and Benjamin - or whose ancestors had been among those Israelites who returned from the Babylonian Exile. People in his audiences who were from the tribe of Naphtali or Dan were just as important as a priest or descendant of David. The Twelve were a clear symbol of the inclusivity Jesus preached and practiced. There couldn't be any women among them because they represented Jacob's twelve sons. Had there been six men and six women, all symbolism would have gone out the window.
Because the evangelists include different names in the three lists of the Twelve, we presume the "group" was more important than its individual members. (When teaching about the Twelve, I ask my classes to name the Three Stooges. Though they come up with six names, each of the six is still a member of the Three Stooges.) Of course, the Twelve only make sense when you're dealing with Jews. That seems to be why John never names them. By the end of the first century he appears to have given up on converting Jews. The Gentile Christians for whom he wrote wouldn't have appreciated the inclusivity of the twelve tribe symbolism.
But on the other hand, this symbolism seems to be why it's important for Luke to get the number back to twelve before the coming of the Holy Spirit. The Spirit's arrival will not only gift them with the ability to reach out to all people (the gift of tongues), it will also operate from the premise that this new, spirit-filled community is a gathering of equals.
The author of I John couldn't agree more. For him, the great leveling force which the Spirit brings arises first from the love God has for us, then from the love we have for God and those around us. "God is love," he writes, "and those who remain in love remain in God and God in them." There can be no exclusivity when love is involved.
Notice how John's Jesus prays for his community during the Last Supper. He presumes they're a unique group of people, just as he's unique. His passion for unity logically comes to the fore. "Holy Father," he prays, "keep them in your name that you have given me, so that they may be one just as we are one." If they're to carry on his ministry, they must mirror his mindset, a mindset which not only bugged many around him, it eventually led to his death. "I gave them your word, and the world hated them, because they do not belong to the world any more than I belong to the world."
As Jesus' followers, we'd best surface the "things" about which he was deeply concerned. Among other things, we should be the most inclusive people on this earth.