Albert Barnes on Mark 4:21

Is a candle brought, etc. A candle is not lit up to be put immediately under a measure, or a bed, where it can give no light. Its design is to give light. So my preaching by parables is not designed to obscure the truth, but to throw light on it. You should understand those parables; and, understanding them, should impart the truth to others also, as a candle throws its beams upon a dark world.

Bushel. In the original, a measure for grain, containing about twelve quarts.

Bed. A couch, either to sleep on at night, or to recline on at their meals. Probably the latter is here meant, and is equivalent to our saying, a candle is not brought to be put under the table, but on it. Mt 23:6.

(1) "bushel" Mt 5:15