The Intra-Trinitarian Covenant as the Starting Point for Paul

In two places, Paul initiates a theological point  by placing the foundation of his doctrine before time. In Ephesians 1:4, he tells us of the choosing of the elect "in Him," that is, in Christ, "before the foundation of the world." And again in II Timothy 1:8-10, he tells us that the elect are the objects of His calling "before the ages began," but which has now been manifested. We see similar phrases used by John in John 17:24 and Revelation 13:8, and by Peter in I Peter 1:20. 

In each case, we see the salvific purposes of God exercised in time, in history, but based on decisions made before time and history. If it was before creation, then in what context did God work out these plans? Within the fellowship of the three Persons of the Trinity, co-eternal and co-equal. Paul tells us of the plan among the Father (such as verses 3 and 5), the Son (verses 3,4, and 5), and the Holy Spirit (verse 13). Thus Paul displays to us that his soteriology is inherently trinitarian; God's purposes could be carried out only by the intimate involvement of all three of the divine Persons. 

I have shown the scriptural glimpses of this intra-Trinitarian covenant, or convenant of redemption, from the Old Testament (such as here and here), but we must also see that it underpins the theology of the New Testament. Among other things, it necessarily precludes any christological heresy denying the Trinity or any of the Persons, or their deity and preexistence, especially the heresy of modalism. But it also shows the step by step purposes of God in the redemption of His people, not for our sake, but because of the Father's love of the Son. Thus, it cannot fail or be undone. The intra-Trinitarian covenant provides a sound basis for the assurance of salvation. that again precludes most of the aberrant sects, who all maintain a fragility of their version of salvation, such that it can be lost at any time.