According to Upanishads, all this creation emerges from Brahman, lives in the Brahman and dissolves in the Brahman.
सर्वं खल्विदं ब्रह्म तज्जलानिति शान्त उपासीत ..... ॥ ३.१४.१॥
III-xiv-1: Verily, all this universe is Brahman. From Him do all things originate, into Him do they dissolve and by Him are they sustained. On Him should one meditate in tranquility.....
..... यतो वा इमानि भूतानि जायन्ते । येन जातानि जीवन्ति ।
यत्प्रयन्त्यभिसंविशन्ति । तद्विजिज्ञासस्व । तद्ब्रह्मेति ।
स तपोऽतप्यत । स तपस्तप्त्वा ॥ १॥
III-i-1: ..... "Crave to know that from which all these beings take birth, that by which they live after being born, that towards which they move and into which they merge. That is Brahman". He practiced concentration. He, having practiced concentration.
You may also refer BG 7.4 to 7.7 and Mundaka Upanishad 1.1.7
Though I don't know much about Pantheism however it looks that according to Pantheism, god and universe are identical - that philosophy/concept seems in agreement but actually Brahman in not conditioned or limited to world/universe only. Brahman is beyond his creation. See the following verses from Srimad Bhagavad Gita:
9.4 This whole world is prevaded by Me in My unmanifest form. All beings exist in Me, but I am not contained in them!
9.5 Nor do the beings dwell in Me. Behod My divine Yoga! I am the sustainer and originator of beings, but My Self is not contained in the beings