The scribe said to him, "Well said, teacher. You are right in saying, 'He is One and there is no other than he.' And 'to love him with all your heart, with all your understanding, with all your strength, and to love your neighbor as yourself' is worth more than all burnt offerings and sacrifices." And when Jesus saw that (he) answered with understanding, he said to him, "You are not far from the kingdom of God." (Mk 12, 32-34)
Jesus answered rightly to the question of the scribe. But the same Jesus refused to give a sign when he was demanded to give a sign.
He answers people who are close to the kingdom or those who are in the kingdom or those who could come closer to the kingdom. But if they question him just to test him then he is not willing to answer them.
So the criterion for Jesus to respond is not to reveal his knowledge or his ability but to the people of right intention.
Here in this passage a scribe is closer to the kingdom.
So to be close to the kingdom is to have right understanding of the basic rules of the religion. The religion has two rules: one relating to the worship and the other relating to the practice.
The true worship is a total (mind, heart and soul) surrender to God.
The true practice is love of the neighbour as oneself.
Being close to the kingdom implies relating to God, neighbour and to self, rightly.
