Text 19

tapamy aham aham varsam
nigrhnamy utsrijami ca
amritam caiva mrityus ca
sad asac caham arjuna

Translation

O Arjuna, I give heat, and I withhold and send forth the rain. I am immortality, and I am also death personified. Both spirit and matter are in Me. 

Commentary by Srila Prabhupada 

Krishna, by His different energies, diffuses heat and light through the agency of electricity and the sun. During summer season it is Krishna who checks rain from falling from the sky, and then during the rainy season He gives unceasing torrents of rain. The energy which sustains us by prolonging the duration of our life is Krishna, and Krishna meets us at the end as death. By analyzing all these different energies of Krishna, one can ascertain that for Krishna there is no distinction between matter and spirit, or, in other words, He is both matter and spirit. In the advanced stage of Krishna consciousness, one therefore makes no such distinctions. He sees only Krishna in everything. 

Since Krishna is both matter and spirit, the gigantic universal form comprising all material manifestations is also Krishna, and His pastimes in Vrindavana as two-handed Shyamasundara, playing on a flute, are those of the Supreme Personality of Godhead.

Commentary by Sri Visvanatha Cakravarti Thakur
(combined commentary for verses 16, 17, 18 and 19)

"How one can worship you as visva rupa in many ways (bahudha)?" The Lord speaks four verses in response.

Kratu means sacrifices mentioned in the sruti like the agnistoma. Yajna refers to sacrifices mentioned in the smrtis like vaisvadeva homa. Ausadham refers to food made from herbs.

I am the father (pita) because I produce the individual and total ingredients for all the universes. I am the mother (mata) because I hold within my womb the universe. I am the nourisher (data) of the universe. I am the grandfather, because I produce the creator of the universe, Brahma. I am the object to be known and the object which purifies.

I am the result (gati), the master (bhartr), the controller (prabhu), the seer of all good and bad things (saksi), the abode (nivasah), the deliverer from dangers (saranam), and the motiveless benefactor (suhrt). I am the act of creation, destruction and maintenance (prabhava pralaya sthanam). I am the treasures (nidhanam) such as padma nidhi and sankha nidhi,4 the cause (bijam), and am indestructible (avyayam), unlike rice and other seeds which are temporary.

Being the sun, I cause heat in the summer, and shower rain in the rainy season, and sometimes I also hold back the rain. I am liberation (amrtam), and repeated birth and death in bondage (mrtum). I am the subtle and the gross (sad asad): Thus the Person, thinking that I am all of this, worships me as the form of universe. These verses are connected thus with the last part of verse 15.