Jesus says in the introduction to his Sermon on the Mount, (Matthew 5-7) “Blessed are the poor in spirit, for theirs is the kingdom of heaven.” This is the primary premise, and the basis of all that will follow. It is the gospel because it proclaims that those who do not deserve heaven can get in!
You may have heard that heaven is something to be earned. Many religions teach, and many people live their lives believing that we must prove ourselves to God. We may assume a kind of Darwinist view of spirituality; survival of the fittest, only the fittest, who deserve heaven, get in. Religions may teach that those who are really worthy, who pay their money, go to church and stuff like that, will enter the kindom of heaven. I’ve heard people dogmatically proclaim that there is nothing free in this life. The doctrine of karma may be like this; we get exactly what our deeds deserve. But Jesus does a reversal, he proclaims that those who do not deserve heaven can get in. This is amazing, and this is why Jesus is so radical. This is why people follow him.
This principle of Jesus means that we can come before God just as we are with no pretense. We come boldly before his throne of grace, we come to the cross for forgiveness. When we see a poor person begging beside the road they are not offering to give us something, they are asking for mercy. When we come to God we are just hitch-hikers catching a ride on Jesus. This is not my assertion or me devising an easy way, it is the rule of Jesus and the way his kingdom works. It is the way I came to God many years ago, and the way I come today.
And what is the kindom of heaven? First and most important, it is relationship with the King. Then it is being wherever he is. There is a large section on the Sermon on the Mount on my blog Ancient Path (see tab at top of page).