Romanos 8:14

‘For as many as are led by the Spirit of God, these are sons of God.'

And one reason why we can be so sure that we ‘will live' is because, by being led by the Spirit in this regard we are demonstrating that we are ‘sons of God'. The assumption is, of course, that in the same way we will follow all the Spirit's leading. And the fact that we can sense His leading is confirmation of the fact of our sonship. The warning is, however, elsewhere given that we can be misled (1Co 12:3; 1 Juan 4:1 ff). We must therefore ensure that our leading is a true leading of the Spirit (there are other spirits which will try to lead us astray including ‘the spirit who now works in the children of disobedience' - Efesios 2:2). In Juan 1:12 those who receive ‘the Word', that is those who believe on His Name, are given the right to be ‘called children of God'. Here that advances to adult sonship. And the idea is that God could never allow His sons, who are destined to be made like His Son (Romanos 8:29), to ‘die' eternally. They are sons for ever (Juan 8:35).

The term ‘son of God' is never unambiguously used of believers in the Old Testament. It rather refers in the plural to the bene elohim (sons of the elohim - angels - as in Job 1-2), but Israel as a whole is called ‘My son' (Éxodo 4:20; compare also ‘Ephraim is my firstborn' - Jeremias 31:9), and individually Israel are seen as ‘the children of the LORD your God' (Deuteronomio 14:1). In Isaías 43:6 God also speaks of the people of Israel as ‘My sons and My daughters', and in Oseas 2:1 LXX (cited by Paul on Romanos 9:26) God speaks of His people as ‘sons of the living God. In a similar way God is seen as the father of Israel rather than of individuals. The kings of Israel were seen as His adopted sons, ‘you are My son, today I have begotten (adopted) you' (Salmo 2:7). Compare also 2 Samuel 7:14 ‘I will be his father and he will be my son'. So the seed thought was there, but not the full reality. Jesus illuminated the idea and took it further, regularly speaking of God as ‘our Father' (see especially the first half of Matthew's Gospel, e.g. Mateo 5:45; Mateo 5:48; Mateo 6:1; Mateo 6:4; Mateo 6:6; Mateo 6:8 etc.) and less often referring to believers as ‘sons' (Mateo 5:45). Jesus Himself was, however, called ‘the Son of God' and ‘the Son' and the probability is that our adopted sonship primarily derives from Him as a result of our union with Him (Hebreos 2:10), supplemented in terms of the further background.