In plain words
From this gross body the subtle prāṇa appears subtler still. Subtler than this is the Manas. Subtler still than the Manas is Vijñāna. Subtler than Vijñāna is Ānanda. From the gross annamaya body have come forth the most subtle prāṇamaya, manomaya, vijñānamaya and ānandamaya lives. Food does not mean only the nourishment we eat. All prāṇamaya substances take shape as food itself. So food itself takes shape as the annamaya form. The eater and the eaten are food itself. Food itself eats food. One creature takes shape as food for another creature. The whole world, in its gross form, appears as annamaya alone. That is why the ṛṣis set forth the principle annaṃ brahma too. To change this annamaya body-principle into a manomaya form and to experience Ānanda in the vijñānamaya: that is man's duty.
Humanness that began with food must end in Ānanda
This Vijñāna is not equal in all living beings. Only some few attain this Vijñāna. Though this manomaya is present even in animals, birds and beasts, which are prāṇamaya, they lack the power of enquiry, and so they cannot attain such a sacred principle of Jñāna. They have lost the weighing of the eternal and the transient; their power to enquire into their own good and bad has come to nothing; and for this very lack of discernment such Vijñāna cannot show itself in animals, birds and beasts. Man alone is the one who exercises the power of enquiry into good and bad and the weighing of things eternal and transient! Such a man alone becomes fit to attain Ānanda and to experience it. That humanness, which began with food, should reach its end in Ānanda: this is its chief duty. This is man's chief goal.