Ephesians 2:19 delivers one of the most compressed reorientations in the New Testament: "Now therefore ye are no more strangers and foreigners, but fellowcitizens with the saints, and of the household of God." Three categories shift in one sentence — you were a stranger, now a citizen; a foreigner, now a household member. The Greek word for household is oikeios — belonging to the same house, the same family. This is not club membership. This is family.
Romans 15:7 provides the mechanism: "Wherefore receive ye one another, as Christ also received us to the glory of God." The word "received" is proselambanomai — to take to oneself, to welcome into one's company. Christ took you to himself. Not as a project, not on probation. Into his company. And that is the standard Paul gives for how believers should receive one another.
John 15:15 captures the intimacy that comes with belonging: "Henceforth I call you not servants; but I have called you friends; for all things that I have heard of my Father I have made known unto you." Servants do not know what the master is doing — they only have instructions. Friends are let into the reasoning. Jesus moved you from the category of executing commands to the category of shared understanding. That is a different kind of belonging entirely.
Commentary is from a charismatic Protestant perspective, drawing on KJV text and public-domain sources including Spurgeon, Andrew Murray, and Matthew Henry.