Why does the Diamond Sutra say that when bodhisattvas practice generosity without abiding in marks, the merit is inconceivable and immeasurable?

Here, "marks" refers to the marks of objective realms—the six sense-object realms of form, sound, smell, taste, touch, and dharmas. When a bodhisattva practices generosity (dāna), he does not abide in the marks of form, sound, smell, taste, touch, or dharmas, nor does he cling to these marks; his mind empties these marks, and in giving, the three wheels are empty. He does not discriminate by the recipient's gender or age, status or rank, poverty or wealth, power or position; nor does he discriminate by appearance, nor by whether the recipient is an enemy or a loved one—he gives equally to all. He also does not calculate or ponder what benefits the giving might bring him from those people, does not expect any return in the form of realms such as form, sound, smell, taste, touch, and dharmas, or wealth, sex, fame, food, and sleep, and still less does he consider the value of the items given, whether precious or cheap. As long as there is someone in need, he gives unconditionally, without calculation or discrimination.

One who can abandon all marks, cling to no marks, and give with the three wheels empty has a vast capacity of mind and is no longer an ordinary person—one whose mind has already been emptied is no longer an ordinary person. Such a one is a great-minded bodhisattva in the true sense, possessing the profound wisdom of the emptiness of marks, a person of great merit. After great generosity, wisdom and merit advance another level. The merit of the wisdom of emptiness is not limited by quantity; the merit thus obtained is immeasurable and boundless, inconceivable. As vast as one's capacity of mind is, so vast is the merit one obtains; merit is directly proportional to capacity of mind, the two mutually reinforcing. As for one who gives while clinging to marks, the mind is constrained and obstructed by marks, so the capacity of mind is small and the merit obtained is slight. How can a small vessel hold many things or large things? Merit follows the vessel: a great vessel brings great merit, a small vessel brings small merit—this is inevitable. Therefore, when a bodhisattva gives without abiding in marks, his capacity is great and his mind is like empty space; the merit he obtains is likewise like empty space—immeasurable, boundless, and beyond estimation.