Gemara:


Ein Ayah:
People forget details because the principles are not well established within them, and therefore the deep view as to how the details emanate from the principles are not natural to their thought process. In contrast, one who acquired a deep and organized understanding of the principles will understand how the details are needed to complete the principle, and then he will not forget the details.
The average person is not on the level to view even the "logical" parts of the Torah with their details as something that must be as it is by logical necessity. However, the most pious people, who maintain a keen understanding of the fundamental ethics upon which the Torah stands, are much more capable of internalizing and thereby remembering the whole body of Torah knowledge.
Because these holy people are very valuable to the world, as they raise mankind from its lowly state of preoccupation with physicality, it is proper that they spend a lot of time each day renewing their spiritual outlook. Therefore, it is proper that they should not have to spend too much time on earning a living, which is why Hashem sends blessing to the work they do. Someone who is not on such a high level does not see such blessing unless he works very hard. This is because generally, toiling at work brings human completeness, as the mishna (Avot 2:2) says: "Torah study goes well with work, for toiling on the two of them distances one from sin." This is why Hashem made it a rule of nature that generally a person will not get the sustenance he needs without hard work, so that he not be affected as much by the proclivity for sin that is in his midst. However, the pious, who have raised their spirit in moral erectness and a have a viewpoint close to that of the holy Torah, are far from sin. Since they do not need the hard work, Hashem can send special blessing to their work.