... tat tvam asi (तत्वमसि ) ...
-Chandogya upanishad, VI.VIII ...

Chandogya Upanishad is also one of the oldest ones and perhaps the best known. It belongs to Saamveda, the veda with metre. It has many very interesting passages in which we learn
- of the knowledge that Kshatriyas had but Brahmins did not,
- of Satyakama's story about how its not your birth that decides if you are a Brahmin,
- of Aruni's statement about the origin of the universe from sat which in the same breath challenges another theory of origin,
- of the extremely ascetic teaching exactly opposite that of the much later Bhagwad-Gita about duty (but the same as what Buddha said just before the rise of Bhagwad-Gita). It is stated that to obtain Moksha one has to give up ordinary life and stay in the forest,
- as to why dead bodies are burnt (rather than, say, buried),
- what and why are the five libations (Agnihotra), etc.

But certainly the most famous part is where uddaalaka aaruNI teaches his son Shvetaketu how he - Shvetaketu - and Brahman are identical. This is where dvaita (a common aspect of most religions) becomes advaita.

VI.VIII: The source of food is water, of water the fire, of fire it is sat (सत or Being or Brahman). That which is the subtle essence, that is True, that is the Self. That art thou (tat tvam asi), Shvetaketu.

VI.IX: Just like bees mix nectar of different flowers and then all the nectar is one, so also all beings are one with the Being. tat tvam asi.

VI.X: Just like rivers become one with the ocean and lose identity, not knowing "I am this river", "I am that river" etc., so also beings can't tell themselves from Being. tat tvam asi.

...

This is Vedic monism at its peak. No external gods needed, not even the One, because you are it. Quiet a few analogies have been used, but so be it.

Just like we are one with the Brahman, we are also one with the problems that surround us. We are also the solutions. Not just charity, but everything begins with ourselves.