He expounded all things to his disciples - That they might be capable of instructing others. Outside hearers, those who do not come into close fellowship with the true disciples of Christ, have seldom more than a superficial knowledge of Divine things.
In the fellowship of the saints, where Jesus the teacher is always to be found, every thing is made plain, - for the secret of the Lord is with them who fear him.
Without a parable spake he not unto them - That is, the things pertaining to his kingdom. On other subjects he spake without parables. On these, such was their prejudice, so many notions had they contrary to the nature of his kingdom, and so liable would plain instructions have been to give offence, that he employed this method to “insinuate” truth gradually into their minds, and to prepare them fully to understand the nature of his kingdom.
They were alone - His disciples.
He expounded - Explained. Showed them more at length the spiritual meaning of the parables.