“Little doubt surrounds the claim that the kingdom of God was central to the message of the historical Jesus. The expression and its equivalents (‘kingdom,’ ‘kingdom of heaven’) occur more than 100 times in the Synoptics alone. The present and future arrival of God’s reign in a new, more powerful way on earth through the mission and ministry of Jesus encapsulates a large amount of what the Gospels remember Jesus as being about. In all of Paul’s letters, however, the term appears only 14 times.
If we examine the Pauline epistles further, we discover that ‘justification by faith’ is often viewed as their central theme, especially in 2 Corinthians, Romans, and Galatians. Throughout Paul’s writings, the noun dikaiosunē (‘justification’) appears 58 times; the verb dikaioō (‘to justify’), 27 times. Compare these figures with 2 and 7 uses in the Synoptic Gospels, respectively, with none of either form in the Gospel of Mark. How do we account for this shift in emphasis? To begin with, the Greco-Roman world would have not been nearly as familiar with the Hebrew concept and background of ‘the kingdom of God,’ so its infrequency in Paul’s letters to diaspora churches should cause no surprise. Second, the Greek term dikaiosunē (‘justification’) also means ‘righteousness’ or ‘justice.’ It is the same noun appearing in the translation of Jesus’s Sermon on the Mount in Matthew 6: 33: ‘But seek first his kingdom and his righteousness, and all these things shall be given to you as well.’ ‘Righteousness’ or ‘justification’ therefore defines what God’s kingdom comprises; the two concepts mesh rather than compete with each other.
Moreover, frequency of usage does not always equate to importance. Many of the Gospel references to ‘kingdom’ come in parallel texts, making the number of occurrences artificially high. The fourteen appearances in Paul are scarcely negligible. In Romans 14: 17, the kingdom of God is defined, in part, as righteousness (dikaiosunē again). In 1 Corinthians 4: 20, the kingdom is about power, reminiscent of the linkage of those two concepts in Mark 9: 1. Four times Paul speaks of someone’s inheriting or not inheriting the kingdom (1 Cor 6: 9, 10; 15: 50; Gal 5: 21), while five times someone in the Gospels talked about inheriting something synonymous with the kingdom— the earth in the age to come (Matt 5: 5) or eternal life (Matt 19: 29; Mark 10: 17; Luke 10: 25; 18: 18). The list could go on. Conversely, righteousness even in the ‘Pauline’ sense of a legal declaration of right standing is scarcely absent from the Gospels. Jesus’s statement at the end of his parable of the Pharisee and tax collector carries the exact sense of many of Paul’s uses: ‘I tell you that this man, rather than the other, went home justified before God’ (Luke 18: 14). Matthew 12: 37, referring to justification or acquittal by one’s words, in the context of Judgment Day, affords another close parallel…
A final comparison draws Jesus and Paul even more closely together. Ephesians 2: 8– 9 reminds us that ‘justification by grace through faith’ is the fuller and more accurate summary of Paul’s key concept. And grace is extremely important to Jesus, even if the word itself appears infrequently in the Gospels. The parable of the prodigal son (Luke 15: 11– 32) forms the classic illustration, but the much less well-known parable of the unworthy servant teaches the flip side equally powerfully— our inability to merit anything from God (Luke 17: 7– 10). Not only are both Jesus and Paul sharply criticized by the religious ‘right wing’ of their day for their views and behavior in this respect; they reply in kind. Jesus and Paul both reserve their sharpest rebukes for the religious insiders who knew better but nevertheless drew the boundaries of their faith too narrowly. John Barclay compares Jesus’s table fellowship with sinners and Paul’s mission to the Gentiles and is struck by their congruity: ‘Both enact and express a paradigm of God’s grace that is simultaneously welcoming to the lost outsider and deeply challenging to the insider— challenging to the point of scorching away the secure marks of a bounded system.’” Excerpts from The Historical Reliability of the New Testament by Dr. Craig Blomberg