The answer is obvious: no one lights a lamp to hide it. Barnes says, "A candle is not lit up to be put immediately under a measure or a bed, where it can give no light." Then he draws out Jesus' point: "So my preaching by parables is not designed to obscure the truth, but to throw light on it."

Jesus had just said that to those outside, "all these things are done in parables" (Mark 4:11). This question shows that hiding is not the goal. Gill says it was not Christ's will that the truth should be "always, and altogether, and from all men" covered with parables, and that His disciples were to be "lights of the world."

Jesus answered with a promise: "For there is nothing hid, which shall not be manifested; neither was any thing kept secret, but that it should come abroad" (Mark 4:22). He called for attention, "If any man have ears to hear, let him hear" (Mark 4:23). Then He warned, "Take heed what ye hear," and promised, "unto you that hear shall more be given" (Mark 4:24-25).

The KJV "candle" translates lychnos, which the interlinear renders "lamp," as the ESV does. The "bushel" is modios, a dry measure; Thayer describes it as "about a peck," and Barnes calls it "a measure for grain containing about 12 quarts." The bed, Barnes says, was a couch "either to sleep on at night or to recline on at their meals," and he thinks the meal couch is meant here.

The Greek has the article with each household item: the lamp, the bushel, the bed. These were things every home had and every listener knew.

Jesus' parables were not meant to lock truth away forever. Some things were hidden for a time (Mark 4:11-12), but God's purpose is that there is "nothing hid, which shall not be manifested" (Mark 4:22). Light is meant to be seen.

Those who receive light are meant to give light. Matthew Henry says, "By his thus instructing them, they were made able to instruct others." Jesus used the same picture in the Sermon on the Mount: "Ye are the light of the world," and "Neither do men light a candle, and put it under a bushel" (Matthew 5:14-15). Luke ties the lamp saying to hearing: "Take heed therefore how ye hear" (Luke 8:16-18). Receiving the word and shining it go together.