Mar 4:29 But when the fruit is brought forth, immediately he puts in the sickle, because the harvest is come.
Alternative: But when the fruit is bestowed, immediately he dispatches the sickle to supply the harvest.

So the earth brings forth fruit from the seed automatically, but to get the benefit of the harvest, the sickle must be used to cut down the wheat. The purpose of the crop is to be productive, so once it has produced fruit, it is time for it to be cut down.

The central character in this parable is the man who sows the seed. Christ says that this man doesn't know how the information in the seed and the nature of the earth combine to bring forth is fruit. So the man in this analogy is every one of us. To survive, we sow the seeds, let the earth do its work, and then harvest the resulting crop. The process in between the sowing and the harvest are God answering our prayer, giving us our bread.

However, this story is a parallel with Christ and his apostles sowing the word. The word "apostle" is even referenced here. The verb describing "sending in" the sickle is the root word for apostle. Those sowing the word may not know how or where it will grow but know that it happens automatically. However, the parallel with the apostles sowing the word seems to seem to breaks down at the very same point the term for "apostle" is mentioned. The apostle does not send in the sickle and harvest the crop at least not in any way that is easy for us to understand.

This last part of the verse is ominous, suggesting as is does the inevitability of death. Symbolically, Christ uses the harvest in Mat 13:39 to describe "the end of the world," or, more accurately, "the end of an age." In my view, for Christ this means our personal physical deaths. Somehow, it is this death that allows the fruit to be harvested.

On the physical level, the death of one generation allows new generations to arise and what is built by one generation is inherited by the next. On the intellectual level, the ideas of one generation bear fruit in the next generation as they build on the best ideas of the previous generation. On the emotional level, the child/parent/grandparent relationship lays the foundation for all personal relationships of caring and the passing of our grandparents and parents teaches us what lives on in those relationships. On the spiritual level, we cannot know what is happening exactly except in the sense of following these parallels.

In Mat 26:46 the term translated here as "is brought forth" is translated as "betrayed" as Christ wakes the apostles when the soldiers come with Judas to arrest him.

"Fruit" is from karpos (karpos), which means "fruit," "the fruits of the earth," "seed," "offspring," "returns for profit," and "reward."

"Is brought forth" is from paradidômi (paradidomi), which means "to give over to another," "to transmit," "to hand down," "to grant," "to teach," and "to bestow."

"Immediately" is from eutheôs (eutheos), which is the adverb of euthus, which means "straight," "direct," "straightforward," and "frank." As an adverb, it means "straight," "simple," "straightway," forthwith," "immediately," "directly," and "at once."

"He puts in" is the Greek, apostellô (apostello), which is our source of the word "apostle." It means "to send off," "to send away," or "to dispatch."

"Is come" is from paristêmi (paristemi), which means "to cause to stand beside," "to place besides," "to set before the mind," "to present," "to furnish," "to supply," "to deliver," "to make good," "to show," "to present," "to offer," and "to render."