Into good ground - The fertile and rich soil.
In sowing, by far the largest proportion of seed will fall into the good soil; but Christ did not intend to teach that these proportions would be exactly the same among those who heard the gospel. Parables are designed to teach some "general" truth, and the circumstances should not be pressed too much in explaining them.
An hundred-fold - That is, a hundred, sixty, or thirty "grains" for each one that was sowed an increase by no means uncommon. Some grains of wheat will produce twelve or fifteen hundred grains. The usual proportion on a field sown, however, is not more than twenty, fifty, or sixty bushels for one.

Good ground - Where the earth was deep, the field well ploughed, and the brambles and weeds all removed. See more on Matthew 13:19 (note), etc., and see on Luke 8:15 (note).
Some a hundred-fold - For the elucidation of this text, I beg leave to introduce the following experiment. In 1816 I sowed, for a third crop, a field with oats, at Millbrook, in Lancashire; the grains weighed, on an average, 3/4 of a grain each. One grain produced three stalks with three ears: the largest had 68 grains in it, the second 26, and the third 25.
Whole number of grains 119, which together weighed 82 grs.
The root separately, after washing and drying, weighed 13 grs.
The stalks and remaining leaves (for many had perished in the wet season) 630 grs.
Weight of the whole produce of one grain of oats 726 grs. which was 725 times and one quarter more than the original weight.
The power of grain to multiply itself, even in the same year, is a subject as much of curiosity and astonishment as of importance and general utility. For the farther elucidation of this text, I shall give the following example from a practice in agriculture, or rural economy, which is termed filtering.
On the 2nd of June, 1766, Mr. C. Miller, of Cambridge, sowed some grains of the common, red wheat; and on the 8th of August a single plant was taken up, and separated into 18 parts, and each planted separately: these plants having pushed out several side shoots, about the middle of September some of them were taken up and divided; and the rest between that time and October. This second division produced 67 plants. These plants remained through the winter, and another division of them, made between the middle of March and the 12th of April, produced 500 plants. They were divided no farther, but permitted to remain in the field. These plants were in general stronger than any of the wheat in the field. Some of them produced upwards of 100 ears from a single root and many of the ears measured seven inches in length, and contained between sixty and seventy grains. The whole number of ears produced from the single plant was 21,109, which yielded three pecks and three-quarters of clear corn, weighing 47lbs. 7oz., and, from a calculation made by counting the grains in an ounce, the whole number of grains was about 576,840. Mr. Miller thinks that, had he made a second division in the spring, the number of plants would have amounted to 2000. Who can help admiring the wisdom and providence of God in this single grain of corn! He has, in some sort, impressed on it an idea of his own infinity; and an idea which, like the subject to which it refers, confounds our imagination and reason. How infinitely great is God, even in his minor works.

But others fell into good ground,.... Not beaten and trodden by the feet of men, nor stony, nor thorny, but well broke up, manured, and tilled; which designs good, honest hearted hearers who become so by the Spirit and grace of God; who with a spiritual understanding, experience, savour, and relish, what they hear; see Matthew 13:23
and brought forth fruit, some an hundred fold, some sixty fold, some thirty fold: some seeds produced an hundred, others sixty, and others thirty. The first of these especially was a large increase, but what was sometimes had, and which Isaac received in Gerar, in the land of the Philistines, Genesis 26:12 and is what Pliny says (g) of Byzacium, a country of the Lybiphoenicians, that it yielded an hundred fold to its husbandmen; and of such fruitfulness was the land of Israel, of which the Jewish doctors say some things incredible: they tell us a story (h) of
"one that sowed a measure of vetches, or pease, , "and it produced three hundred measures"; they say unto him, the Lord hath begun to bless thee, &c.''
Here, in the parable, these various increases intend the different degrees of fruitfulness in gracious souls; for though the fruits of grace, in believers, are of the same quality, yet not of the same quantity. Some believers are grown to a greater maturity than others; some are but little children, some are young men, some are fathers.
(g) Nat. Hist. 1. 5. c. 4. (h) T. Hieros. Peah, fol. 20. 2.

But others fell in good ground. The goodness of this last soil consists in its qualities being precisely the reverse of the other three soils. It was not hard, stony, or weedy.
Some thirty, some sixty, some a hundred. Thirty-fold is now really a first-rate crop, even for such plains as Esdraelon, just below Nazareth. But in the time of Christ there might be realized, in favorable circumstances, a hundred-fold. Intelligent gentlemen (in the plain of Esdraelon) maintain that they have themselves reaped more than a hundred-fold.--Land and Book.

Good ground - Soft, not like that by the highway side; deep, not like the stony ground; purged, not full of thorns.