Luke 8:10

‘And he said, To you it is given to know the mysteries of the Kingly Rule of God, but to the rest in parables, that seeing they may not see, and hearing they may not understand.'

Then He explained to His disciples that for them the ‘secrets of the Kingly Rule of God' would be unlocked, because they genuinely wanted to know. The word ‘mystery' in the New Testament always speaks of ‘a mystery now to be revealed'. Thus He would open up the mystery for those who were seeking. And it would mean more to them because they had first had to think about it before asking.

But to the remainder it was told in parables, so that they would see what was on the surface but not see what lay underneath, so that they would hear what was said and yet not appreciate its true meaning. And why should He do this? So that they might not become hardened to the message. Once they really began to want to know they could come and ask. Until then it was better if they only received hints of it.