The explanation comes from the New Dynamic Translation (NPD).
The text shows who becomes God's heir.
_________________
In contemporary ecclesial teaching, one can encounter the claim that all people are children of God. However, such a view is false because it has no support in Scripture. Only a person who is born spiritually, i.e., of God's Spirit, is a child of God. Jesus clearly stated that without the "new birth," that is, without the "spiritual birth" (Gr. gennethe anothen means "born from above" and thus "born of God's Spirit") that leads to a life of divine glory, no one has a chance for an inheritance in the Kingdom of God (cf. John 3:3). Thus, the so-called new birth is an absolutely necessary condition for eternal fellowship with God, who is a Spiritual Being (cf. Jn 4:4). However, the question arises: is it a sufficient condition? Many interpreters say yes. To illustrate this, they cite the example of a child born into a family and show that no matter what the child does, how it acts or what it engages in, it will always be its father's child. They claim that nothing and no one can change this fact. This comparison is highly suggestive, but unfortunately it does not stand up to critical analysis based on the principles of biblical hermeneutics.
There are a few different words in the Bible that are translated the same way in Polish: "child" or "son." However, in the original, their meaning is not the same. Traditional literal translations of the Bible usually do not help in understanding this issue because they translate the words teknon and nepios, paidion and neaniskos, and hyios as "child" or "son" without at all developing the meaning contexts that these words have in Greek.
The word teknon (from the verb tikto, meaning "bearing fruit") is used most frequently (99 times) in the NT to mean a small, newborn child (neonate) who is completely dependent on others and subject to the head of the family. The word could easily be translated "babe," "child," "baby," "child," "kid," which would even better reflect the age described and the characteristics belonging to it. Another word of similar meaning is nepios (15 occurrences in the NT).
The word paidion (occurs 52 times in the NT) is derived from pais (paidos - 24 occurrences in the NT), which is a general term for a subadult - either male or female - who is in a formative stage of development. He is not mature, i.e., not yet formed enough to take over the inheritance. The very word paideuo (13 occurrences in the NT) refers to the process of education (training, coaching), while paideia (6 occurrences in the NT) is a term for a system of education, as we read in Heb 12:5.7.8.11. It is interesting to note that a paideion did not have to be a child born into a particular family, unlike a teknon. A paidion could be an adopted child or a child taken into service (such as the old Polish squire), thanks to which he became a part of the entire educational system, to which all children growing up in a given home were subject.
In the course of his development, Paidion became a neaniskos - a young man full of strength and vigor who could already successfully serve others with his help. For this reason the word was sometimes used to describe young servants. However, he was still in the process of being raised and prepared to take on the role of full-fledged heir - hyios.
The word hyios (382 occurrences in the NT) has a special meaning in the NT. It describes a mature offspring who, having gone through the whole process of education, already has his character and personality formed in such a way that he is prepared to assume his inheritance. Hyios was fundamentally different from teknon and paidion. Not only was he older than them (he had to be over 20 years old), but because he was already mature and proven (for he had successfully passed the various tests and trials to which he was subjected), he was eligible for the formal legislative process of being recognized as a legitimate heir. The procedure of recognition as an heir was called usinization, or in fact, making an heir. It is worth noting that the term "usinization" (Gr. hyiothesia) is closely associated with recognizing someone as hyios, and not as teknon, nepios, paidion or neaniskos. Only after such legalization did someone who had previously been considered an infant, child, or youth in a given family become a full-fledged heir. It is with the word hyios that the Scriptures define Christ during His earthly ministry, thus indicating that He became the first of those who, by His example, are to reach the position of hyios.
Lack of understanding of this important socio-cultural-historical context leads many interpreters to conclude (often on the basis of their own perceptions or cultural-family experiences) that man, in becoming a child of God (Gr. teknon) - thanks to the spiritual birth (the so-called new birth) - immediately becomes an heir (Gr. hyios) with full access to God's inheritance. In their theses, however, these commentators forget about an extremely important stage of being rooted in Christ, about the necessity of forming in man a character like that of Jesus, about growing in wisdom, obedience and faithfulness to God. It is this stage that the Apostle Paul calls the process of sanctification, and the author of the Letter to the Hebrews calls paideia. The author of the Letter to the Hebrews calls it paideia. In fact, he also draws on Paul's terminology when he writes that "without sanctification no one will see the LORD" (Heb 12:14). (cf. Heb 12:14 NPD). Accepting the idea that immediately upon conversion (repentance) people become full-fledged heirs of God's kingdom for eternity is not supported by God's Word. For it would mean that salvation (rescue from the power, influence, and consequences and presence of sin) is a one-time (and at the same time final) event in everyone's life, while God's Word attests that it is a process. To accept the concept of "once saved forever saved" would mean that a person would be immediately hyios after the new birth, and this is in complete opposition to what the Bible teaches. The starting point of the race that the Apostle Paul writes about in Acts 20:24 and Phil 3:12-14 would also be the finish line. Utter nonsense.
The entire Word of God clearly communicates that the only legitimate heir to the fullness of God's blessing, God's wisdom, holiness, and glory is Jesus Christ alone (cf. John 5:39; Eph. 1:3-14; and Col. 1:13-20). And believers have access to all of God's riches and glory of salvation only IN CHRIST. Only in Him and only through Him all the blessing of Heaven is open to them and is at their disposal. The condition of the access to the indestructible inheritance in the Heavens is staying in CHRIST and not deceiving oneself with the conviction about the supposed power of some single prayer inviting Jesus to life, which is treated almost as a magic spell. Of course, a person's decision to precede such a prayer has meaning and significance only if it expresses sincere submission to the will of the Most High and acceptance of His plan of salvation. But if such a prayer is not preceded by repentance, if it is not followed by sorrow, repentance, and adherence to God's Word for the purpose of transforming one's life - sanctification (which is a sign of a full and complete orientation toward Christ) - then it (prayer) is just another form of acquiring a religious "insurance policy" that has nothing to do with the new creation and personal growth to the status of hyios in the process of sanctification.
Wishful religious thinking is often supported by false notions of God's childhood. Unfortunately, reliance on the "magical" power of religious observances (cf. 1 Cor 1:14), which supposedly can replace personal growth in wisdom and grace (cf. Lk 2:52) and in sanctification (cf. Heb 12:14), has been present in the life of Christian communities from the very beginning of the formation of Christianity. The Apostle Paul encountered this problem in Corinth, as we read in 1 Cor 3. In this chapter, the Apostle admonished the Corinthians for behaving like nepios, and then (in verses 18-21) went on to teach the need to grow in wisdom and sanctification. In verse 1 Corinthians 3:17 Paul gives a strong warning, coinciding with the one God put in the mouth of the prophet Isaiah: "Woe to rebellious children who go against my plan" (Isaiah 30:1 NPD).
The apostle Paul also wrote about this in his Letter to the Romans. In Romans 8:19, he pointed out that all of creation awaits the revelation of who is indeed God's heir (hyios), and that all of God's children (teknon) are called to the glory that has been prepared for them by the Most High.
Also, the Apostle John in 1 John 3:2 points out that born-again spiritual believers are now tekna (born-again children), but it is not until there is a visible growth in them in Christ-likeness (i.e., hyios status) that they will see Him for what He is (and thus face to face - cf. 1 Cor 13:12). The apostle goes on to use the word paidia (cf. 1 John 3:7) indicating that those who have become teknon must go through a stage of education (paideia) in order to become hyios in the future in the likeness of Christ (cf. 1 John 3:8).
Also, the Apostle Peter in 1 Peter 1:14 points out that newborn believers (tekna) are called to a life of obedience leading to sanctification. This was the path that Christ walked, showing everyone how, being God's child, to grow up to be an heir (hyios).