The Doctor: His Blood Is Thicker Than Ours

Can you say quite honestly that you have a deeper affection for, and a deeper understanding of, you fellow Christians that you have for your natural relatives who are not Christians?  That is a very good test of our position as Christian people.  It is a proof of your regeneration, and it is also a proof that you have paid heed to this exhortation and are putting it into practice.  A Christian should feel a closer bond with another Christian than he feels with a relative who is not a Christian.  This is true of necessity.  The new nature is in us.  We are all children of God and belong to the family of God.  And this is a relationship that will not only last while we are in this world of time, but will last throughout eternity.  – D. Martyn Lloyd-Jones, Romans Vol. 12, p. 352