The things that support everything from within cannot be broken by material force.
What is the "real thing" that does not change and does not lose its existence, as mentioned in the previous section? Krishna says that everything that permeates all things is immortal.
In the annotation, "everything" refers to all material things, such as the body, senses, mind, experiences, and places. The soul that supports them from within permeates everything. And any physical force that can harm the body cannot reach its indestructible essence. It indicates that there is an unchangeable foundation within the changes of all forms.
Japanese Translation from the Geeta Press Edition - Chapter 2, Section 17: "That Which Pervades the Universe and is Immortal"
In the previous section, it was stated that "existing things" do not cease to exist. Now, the speaker is about to begin describing what those "existing things" are.
Sanskrit original text
अविनाशि तु तद्विद्धि येन सर्वमिदं ततम् ।
विनाशमव्ययस्यास्य न कश्चित्कर्तुमर्हति ॥ १७ ॥Romanization
avināśi tu tad viddhi yena sarvam idaṃ tatam |
vināśam avyayasyāsya na kaścit kartum arhati || 17 ||Know that only what pervades this universe is immortal. No one has the power to destroy this indestructible reality. (17)
In this section, "Idam" refers to all material things, such as the body, sensations, mind, and all objects of pleasure, along with places of enjoyment.
All these things, which are included in the common meaning of "material," are permeated by the supreme spirit that represents the principle of life or consciousness.
The subject characterizes the supreme spirit as immortal, thereby indicating that the word "immortal" refers to the same supreme soul that was defined under the name Sat in the preceding section.
It is recognized by those who see the truth as the only "existing" entity.
"No one has the power to destroy this indestructible entity," the master indicates that: Just as clouds are permeated by ether, all material objects are permeated by the Supreme Spirit. Therefore, no material object possesses the ability to destroy this Supreme Soul.
Therefore, only a certain and constantly existing soul represents what is called "existence."