The principle of "gathered together" for an assembly is shown indirectly here, but is clearly stated in the scroll of 1 Corinthians. The real context for Christians to be gathered under His Name alone in on the chapters 1,2,3 of I Corinthians. These would be the teaching of the gathering together unto His name alone if you read carefully. "I am from Apollos. I am from Paul. I am from Peter." 1 Corinthians 1:12 - 17 "Some of you are saying, “I am a follower of Paul.” Others are saying, “I follow Apollos,” or “I follow Peter,” or “I follow only Christ.” Has Christ been divided into factions? Was I, Paul, crucified for you? Were any of you baptized in the name of Paul? Of course not!"
We, as Christians, should be gathered together in One Name-- The Lord Jesus Christ--and not under any name of denominations, organizations, or man made religions. Matthew 18:20 is the principle foundation of the local assembly. It is here that everything stops. It is here that all denominations of today become speechless. It is here that the doctrine of gathering is presented on a firm foundation: The Head Christ, the Rock. Everything else is built on shaky sand.