For if men are controlled by their earthly natures, they give their minds to earthly things. If they are controlled by their spiritual natures, they give their minds to spiritual things.
You, however, are not devoted to earthly, but to spiritual things, if the Spirit of God is really dwelling in you; whereas if any man has not the Spirit of Christ, such a one does not belong to Him.
In other words, it is not the children by natural descent who count as God's children, but the children made such by the promise are regarded as Abraham's posterity.
See what marvellous love the Father has bestowed upon us –that we should be called God's children: and that is what we are. For this reason the world does not recognize us– because it has not known Him.
The man who obeys His commands continues in union with God, and God continues in union with him; and through His Spirit whom He has given us we can know that He continues in union with us.