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.

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.

But without a parable spake he not unto them: and when they were alone, he (l) expounded all things to his disciples.
(l) Literally, "loosed", as you would say, explained to them the hard riddles.

But without a parable spake he not unto them,.... For the above reason, as well as for the accomplishment of Scripture; See Gill on Matthew 13:34, Matthew 13:35.
And when they were alone, he expounded all things to his disciples: after they returned with him from the sea side, to the house in Capernaum, where he usually was when there; see Matthew 13:36. The multitude being dismissed, he unfolded and explained all these parables to his disciples, and led them into a large knowledge of himself, and the mysteries of the kingdom of heaven; whereby they were furnished for the work he had called them to, and designed them for.

But without a parable spake he not unto them--See on Matthew 13:34.
and when they were alone, he expounded all things to his disciples--See on Mark 4:22.

Without a parable, etc. See notes on Matthew 13:36-43.