According to the Gospel writers, Jesus understood his reason for being as to proclaim the Kingdom of God (Luke 4:43). ‘Realm of God’ is a less gender-specific term, so I will use it here.
It is a mistake to think that Jesus was talking about a place. The Realm of God is not synonymous with ‘heaven’ or the ‘new Jerusalem’ or some ‘new’ earth that will be created after some cataclysmic second coming. “The Realm of God,” said Jesus, “is near” (or “here” – it can be either – Mark 1:14). In other words, the Realm of God is a present reality, not something reserved for some unspecified future. Jesus proclaimed it to be at hand; available to be experienced by people now.
One simple way that the Realm of God has been explained is that it exists wherever God is king, i.e. wherever God is ruler; the primary director of our lives. Furthermore, the experience of living in the Realm of God, or allowing G-O-D to be the prime motivator of all that you do, is a fulfilled existence named, in the language of the Gospels, “eternal life.”
For the most part, Jesus used stories to create an impression of the Realm of God, perhaps because the concept he was trying to communicate was too difficult to grasp or because the language did not possess the necessary words. Whilst it may have been difficult to tell people what the realm of God is, Jesus made clear what prevented one’s participation in it; namely, anything that one put ahead of God as an influence in one’s decision-making; e.g. money or family. He also was clear about how to attain it; namely, by giving up everything.
When Jesus speaks about the Realm of God, and Buddha refers to Nirvana, they are talking about much the same thing, Nirvana being the highest state of personality that someone can attain, a state of enlightenment in which a person’s individual desires and suffering go away; a transformed state of consciousness characterised by peace, deep spiritual joy, compassion, and a refined and subtle awareness. Negative mental states and emotions such as doubt, worry, anxiety, and fear are absent from the enlightened mind. (https://tricycle.org/magazine/nirvana-2/).
One thing that is obvious about the way to the Realm of God or to ‘eternal’ life is that it is extraordinarily difficult. This is perhaps the biggest reason to have a church: so that people can seek the Realm with the support of one another. The faith that is required is enormous, the risk is incalculable, the life style too radical to be practical for a solitary individual in our society, and the persistence required needs a ‘cheer squad’ to keep one at it.
For all the difficulty, Realm of God is the ultimate goal of a follower of Jesus. There is a tendency to substitute other very good aims, such as helping the poor, fighting injustice or working for peace instead of going on the personal journey to the Realm of God, simply because people either don’t understand Jesus’ message or they do understand, but find it too difficult even to imagine themselves being able to do that which is required. It is a good thing to help the poor, et al, but such actions would necessarily evolve as a result of a person finding the Realm of God; they are not a substitute for it.