Romans 8:14-18

For as many as are led by the Spirit of God, they are the sons of God.

For ye have not received the spirit of bondage again to fear; but ye have received the Spirit of adoption, whereby we cry, Abba, Father.

The Spirit itself beareth witness with our spirit, that we are the children of God:

And if children, then heirs; heirs of God, and joint-heirs with Christ; if so be that we suffer with him, that we may be also glorified together.

For I reckon that the sufferings of this present time are not worthy to be compared with the glory which shall be revealed in us.