Romanos 8:16

God has provided the believer with two witnesses to his or her salvation, the Holy Spirit and our human spirit (cf. Deuteronomy 17:6; Matthew 18:16). The former witness is objective in Scripture and subjective (cf. Romans 8:14), while the latter is only subjective. Another view is that the Holy Spirit bears witness to God when we pray (Romans 8:15). [Note: See Griffith Thomas, St. Paul’s Epistle . . ., pp. 216; and Robert N. Wilkin, "Assurance by Inner Witness?" Grace Evangelical Society News 8:2 (March-April 1993):2-3. ] Incidentally, this second reference to "spirit" is probably the only one in Romans 8 that is not a reference to the Holy Spirit.

The term "children" identifies our family relationship based on regeneration whereas "sons" stresses our legal standing based on adoption. We are both God’s children, by new birth, and His sons, by adoption.