One of the heresies which prevails in a large part of modern Christendom is the concept that Jesus did not organize a Church or set up a formal and visible kingdom through which salvation might be offered to men. This poorly translated verse is one of those used to support the erroneous concept that the kingdom of God is wholly spiritual; that it is made up of those who confess Jesus with their lips, regardless of what church affiliation they may have; that the kingdom of God is within every person in the sense that all have the potential of attaining the highest spiritual goals; and that baptism, the laying on of hands, Eucharist, marriage, and other sacraments, ordinances and laws are not essential to the attainment of salvation.
The contention of some critics that the Savior by these words taught that the kingdom of God is merely an inner, spiritual condition in the human heart, must very definitely be rejected. Such a condition may qualify for entrance into the kingdom, but it is not itself the kingdom … It is not … a state of mind … nor a disposition of men. The kingdom of God is a fact of history, not psychology … Jesus speaks everywhere of men entering the kingdom, not of the kingdom entering men” (Norval Geldenhuys, op. cit., pp. 443-444).
In the New Testament the term “Kingdom of God,” although used frequently (Matthew uses the phrase “Kingdom of Heaven”), is a very complex idea. Usually the word has one of three meanings: the internal, invisible Kingdom; the social and visible Kingdom; or the final, triumphant Kingdom of God.
The internal Kingdom of God is the reign of God in the hearts of men by His grace. It comes unawares and is within the souls of men (Luke 17:21), and consists not “in food and drink, but in justice and peace and joy in the Holy Spirit” (Rom. 14:17). The visible Kingdom of God is the Catholic Church founded by Christ. It is for all men, contains even sinners, who will someday be cast out, grows from small beginnings (Matt. 13), and is a gift of God’s love (Luke 12:32). The final Kingdom of God is the triumphant reign of God and His Christ. When Our Lord shall return in glory at the end of the world, the Kingdom shall reach consummation (Rev. 19:11-16). Christ instructed His followers to pray for God’s reign to be perfect and complete (Matt. 6:10). Then, at the time of the resurrection of the dead, when the Kingdom is perfect, Christ will deliver it over to God the Father, and God will be all in all (1 Cor. 15:24, 28).
Pope John Paul II further clarified the issue on the Kingdom of God in relation with Jesus and his mystical body, the Church:
As I wrote in the Encyclical letter Redemptoris Missio, “the Kingdom of God is not a concept, a doctrine, or a program subject to free interpretation, but is before all else a person with the face and name of Jesus of Nazareth, the image of the invisible God . . . One may not separate the Kingdom from the Church. It is true that the Church is not an end unto herself, since she is ordered towards the Kingdom of God of which she is the seed, sign and instrument. Yet, while remaining distinct from Christ and the Kingdom, the Church is indissolubly united to both” (n. 18).
To sum up and simplify everything, when we individually and collectively do the will of God as revealed by Jesus and taught by the Church we proclaim, build up, and spread the Kingdom of God, “an eternal and universal Kingdom: a kingdom of truth and life, a kingdom of holiness and grace, a kingdom of justice, love and peace” (Preface for the Feast of Christ the King).
Jesus invites us to enter the kingdom of God which is intended to accept men and women of all nations and ages, but he also asks for a radical choice: to gain the Kingdom, one must believe in Jesus and the One who sent him for our salvation (Jn 17:3; see also Dei Filius (Denzinger-Schönmetzer, 3012)), give up everything (Cf. Mt 13:44-45; 22:1-14) deny oneself and take up one’s cross and follow him (see Mt 16:24). Words are not enough, deeds are required (Cf. Mt 21:28-32) especially “loving one another as He has loved us” (Jn 13:34; cf. 1 Jn 3; 4). This commandment summarizes all the others, and expresses his entire will ( see CCC 2822).