Baptist Hermeneutics 101: The apostolic use of Joel 2 in Acts 2 is governed by the same christological and new-covenant lens that shapes Jesus’ citation of Isaiah 54:13 in John 6:45 (cf. John 1:12–13). “Children” does not mean that every carnal seed of believers automatically inherits the covenant promise. Jesus explicitly identifies those who are “taught by God” as the elect who come to the Father through Him by faith (John 6:45). Baptists therefore conclude that the covenant sign is not administered merely in view of having a believing father. As John 1:13 states, true children of God “were born, not of blood nor of the will of the flesh nor of the will of man, but of God.” Baptism is given to those who call upon God as Father through Christ by the Spirit. Abraham’s children are spiritual and of faith (Gal 3:6–9). Both Joel 2:32 and Acts 2:39 close with the same decisive qualification of these “children”: they are “the called” who receive the promise of the Spirit.

R.B.C. Howell is simply outstanding on the proleptic nature of membership in the covenant of grace/new covenant pre-Christ, and the formal inauguration of this covenant in Christ's person visibilized through the ordinances/sacraments: "Men, eminently pious, deeply imbued with the spirit of true religion, existed in every age; not among the Jews only, but also among the Gentiles. They were all believers in the Messiah promised as yet to come. But they were not visibly organized as the kingdom or church of the Redeemer. The gospel covenant, which was their guide and support, has existed, as we have seen, from 'before the foundation of the world' (Eph 1:4). It is, therefore, really the oldest of all the covenants. It is consequently called the New Covenant, not in respect of the date of its origin, but of the period of its visible administration, which did not commence until after the Old Covenant had served its purposes, was fulfilled, and had passed away. For all that concerned holiness and salvation, it was, nevertheless, fully as effective immediately after the fall, as it is at this hour. Christ Jesus was '... the Lamb slain from the foundation of the world' (Rev 13:8). All who, in any age, have been saved, have obtained their deliverance through faith in him. Up, however, to the time of his personal appearing upon earth, there was no formal outward organization. The only external administration was legal and typical. To anyone who will maturely examine the subject, these facts must be apparent. Readily may you trace the approach of the church to the period of its visibility. Previous to the advent, the covenant and kingdom of Christ are ever spoken of as being in the future. By Ezekiel, Jehovah said, '...I will establish unto thee an everlasting covenant' (Ezek 16:60). And, in another place, '...I will bring you into the bond of the covenant' Ezek 20:37). By Daniel he said, '...[I]n the days of these kings [the Roman Emperors] shall the God of heaven set up a kingdom, which shall never be destroyed: and the kingdom shall not be left to other people; but it shall break in pieces and consume all these kingdoms, and it shall stand forever' (Dan 2:44). Thus did all the prophets speak of the church, up to that moment when the Old Testament dispensation was closed. The kingdom was not yet formally inaugurated. You open the New Testament, and what do you there find? John the Baptist comes, '...preaching in the wilderness of Judea, and saying, Repent ye: for the kingdom of heaven is at hand' (Matt 3:1-2). 'Messiah the prince' (Dan 9:25) appears. He is recognized in his baptism, as the 'Son of God' (See: Matt 3:16-17). Having entered upon his ministry, he proclaims of the kingdom, '...[I]t is nigh, even at the doors;' (Matt 13:29) at this moment, '...the kingdom of God is within you' (Luke 17:21). To which an apostle adds, '...[N]ow is come ... the kingdom of our God....' (Rev 12:10). It may be instructive to mark the precise point of time at which the church of Christ became a visible organization. To do this we must ascertain what it is exactly which places the church in this visible state. It is, as you will at once see upon reflection, not spirituality, nor orthodoxy, nor both these together, but external form. Without spirituality, and orthodoxy, there can certainly be no true church. They are essential to its very existence. Yet these alone do not constitute its visibility, since in that case it would have been visible long before the days of Abraham. And there are many men eminently pious, in the present day, who, whatever may be their devotion to God, are not literally connected with the visible church; which could not be the case if spiritual qualities only were necessary to that union. What more is required, then, to make these good men members of the church? They must, I answer, be baptized and receive the Lord’s Supper. These ordinances, therefore, mark the line of separation between the church and the world. In the truth of this statement, we have, happily, the concurrence of every denomination of Christians. They all teach that those who are baptized and received at the Lord’s table are thus united with the church, and that those who are not so baptized and received, whatever may be their piety or excellence in other respects, are out of the visible church. These ordinances, doubtless, do not draw the line of distinction between the church and the world exactly where God will place it at the last day, because they are administered by fallible men who are liable to mistake the claims of those who receive them. Many, we have reason to fear, are in the visible church, who will not, at the last day, be found on the right hand of the Judge; and many are probably not in the visible church, who will have a place then in the church triumphant. It is nevertheless true that the ordinances, usually called sacraments, mark the established boundaries between the world and the visible church."