The entanglement of the living entity in sense enjoyment is very nicely explained in these verses. The word saṁvatsara, meaning “the progress of time,” is significant. Day after day, week after week, fortnight after fortnight, month after month, year after year, the living entity becomes entangled in the chariot’s progress. The chariot rests on two wheels, which are pious and impious activities. The living entity attains a certain position in life in a particular type of body according to his pious and impious activities, but his transmigration into different bodies should not be taken as progress. Real progress is explained in Bhagavad-gītā (4.9). Tyaktvā dehaṁ punar janma naiti: one makes real progress when he does not have to take on another material body. As stated in Caitanya-caritāmṛta (Madhya 19.138):

eita brahmāṇḍa bhari’ ananta jīva-gaṇa
 caurāśī-lakṣa yonite karaye bhramaṇa

The living entity is wandering throughout the entire universe and taking birth in different species on different planets. Thus he moves up and down, but that is not real progress. Real progress is getting out of this material world altogether. As stated in Bhagavad-gītā (8.16):

ābrahma-bhuvanāl lokāḥ
 punar āvartino ’rjuna
mām upetya tu kaunteya
 punar janma na vidyate

“From the highest planet in the material world down to the lowest, all are places of misery wherein repeated birth and death take place. But one who attains to My abode, O son of Kuntī, never takes birth again.” Even if one is promoted to Brahmaloka, the highest planet in the universe, he has to come down again to the lower planetary systems. Thus he is wandering up and down perpetually, under the influence of the three modes of material nature. Being illusioned, he thinks he is making progress. He is like an airplane encircling the earth day and night, incapable of leaving the earth’s gravitational field. Factually there is no progress because the airplane is conditioned by the earth’s gravity.

Just as a king is seated on a chariot, the living entity is seated in the body. The sitting place is the heart, and the living entity sits there and engages in the struggle for existence, which goes on without progress perpetually. In the words of Narottama dāsa Ṭhākura:

karma-kāṇḍa, jñāna-kāṇḍa, kevala viṣera bhāṇḍa,
 amṛta baliyā yebā khāya
nānā yoni sadā phire, kadarya bhakṣaṇa kare,
 tāra janma adhaḥ-pāte yāya

The living entity struggles very hard due to the influence of fruitive activity and mental speculation and simply gets a different type of body life after life. He eats all kinds of nonsense and is condemned by his activities of sense enjoyment. If one really wants to progress in life, he must give up the ways of karma-kāṇḍa and jñāna-kāṇḍa, fruitive activities and mental speculation. Being fixed in Kṛṣṇa consciousness, one can become free from the entanglement of birth and death and the vain struggle for existence. In these verses the words mṛga-tṛṣṇāṁ pradhāvati are very significant because the living entity is influenced by a thirst for sense enjoyment. He is like a deer that goes to the desert to search out water. In a desert an animal simply searches in vain for water. Of course there is no water in the desert, and the animal simply sacrifices his life in an attempt to find it. Everyone is planning for future happiness, thinking that if he can somehow or other reach a certain point he will be happy. In actuality, however, when he comes to that point he sees that there is no happiness. He then plans to go further and further to another point. This is called mṛga-tṛṣṇā, and its basis is sense enjoyment in this material world.