Yagyavalka rishi when leaving the home for sanyas gave the knowledge of souls to his wife maitreyi therefore this soul gyan is called maitreyi gyan .

In fact vedas contain the whole knowledge of karm gyan and upasana and therefore they do not insist much on knowing about the universe forming or the brahman and leave it to science .

ko addhā veda ka iha pra vocat kuta ājātā kuta iyaṃvisṛṣṭiḥ |
arvāgh devā asya visarjanenāthā ko veda yataābabhūva ||
iyaṃ visṛṣṭiryata ābabhūva yadi vā dadhe yadi vā na |
yo asyādhyakṣaḥ parame vyoman so aṅgha veda yadi vā naveda ||6,7/129/10mndlm rigveda

Who verily knows and who can here declare it, whence it was born and whence comes this creation?
The Gods are later than this world's production. Who knows then whence it first came into being?
 He, the first origin of this creation, whether he formed it all or did not form it,
Whose eye controls this world in highest heaven, he verily knows it, or perhaps he knows not.

Maitreyi gyan tells the relation of soul to soul eg. A  wife soul to a husband soul and similarly for other relations too .

This whole world is governed by souls and stronger souls take the refuge on weaker souls and thus the person acts accordingly .

There is a strong and long duration of relation in wife and husband souls therefore it is said to be continued to 7 births .

Coming to right or wrong births depend upon the deeds performed during previous birth therefore human life is said to be one and only one deciding  life for betterment .

Souls  in environment can be contacted  and called by a human soul  under maitreyi gyan .

As per yajurveda Suryo brahman . The brahman which is  unimaginable can be quoted as sun . Sun illuminates on one side of the moon while the other side is dark . So two type of pleasures are there , 1. Chidanand  2. Sadananda .

study starts with material as science , rises then to logical philosophy giving the thought to spirituality and finally theology comes as devotion .

Thirteen  devas as 1. Brahma 2. Rudra 3.chandra 4. Dic 5. Agni 6. Vayu 7. Indra 8. Surya 9. Upendra 10. Varuna 11. Prajapati 12. Ashvini 13. Mrityu and all pervaded by vasudeo 14 . the parmatma .

Here two pleasures chidananda , eternal pleasure as full moon and sadananda , the eternal rest as full dark moon is taken . In detail we can refer to ved-richas by bhagvatam and gita as follow :

What they [karma-kânda] enjoin [to be done], what they [upâsana-kânda] indicate [as being the object of devotion], what aspects they describe or what alternatives they [jñâna-kânda] thus literarily offer [as philosophy], the heart of this matter is in this world not known by anyone else but Me . I am the object of worship, the concern of the enjoined action and the alternative that is offered and explained away . The transcendental sound vibration of the Vedas establishes Me as being their meaning and elaborately describes the material duality as simply being the illusory one has to emasculate to ultimately become happy.' Bhagvatam 42 , 43 /21 / 11 canto

Attaining to the lunar light by smoke, night-time, the dark fortnight or the six months of

the southern path of the sun (the southern solstice), the Yogi returns.

 The bright and the dark paths of the world are verily thought to be eternal; by the one

(the bright path) a person goes not to return again, and by the other (the dark path) he returns.

 The bright path is the path to the gods taken by devotees. The dark path

is of the manes taken by those who perform sacrifices or charitable acts with the expectation of rewards. Gita 25 , 26 /8 ch