this translation is quite poor. while "whole" is an acceptable definition of purna which means full (and complete/whole/infinite but also by implication perfect and self-fulfilled) i dont know where they are getting "is all that is visible" and "is all that is invisible". idam is just "this" and adah is just "that". that is full, this is full. (in the upanishads that refers to God and this to the universe) "was born out of" is not a very good translation of udacyate either which means comes forth/proceeds/arises. there is a sense of timelessness here where material and efficient cause is conveyed with a lack of specificity as to exactly how creation unfolds (no specific mention of emanating/manifesting/projecting/being born, these are all just approximate synonyms). so, from the full the full arises. perhaps the most egregious part to me is "when the whole is absorbed into the whole". adaya means "having taken", of the full the full having taken. (having taken the full from the full) i would insist on this translation over "is absorbed" because having taken refers directly to the creation of the universe from God but also definitely refers to the dissolution of the universe in God. because the full alone remains (actually eva is an intensifier particle, so its closer to meaning "indeed" or "verily", while "alone" magnifies based on context), Brahman can be described as remaining undepleted when the universe proceeds from Him and as still being perfect when the universe ceases to exist (or more accurately for most hindus, exists in a causal seed state within God. but for me, God itself is the causal agent and source material, even the seed too dissolves into Him. this may be semantics though)

so a much better translation would be "that Brahman/God) is full, this (the universe) is full. from (that) full, (this) full arises. having taken the full from the full (referring specifically to creation but also to dissolution), the full indeed remains."

the meaning: God is full/complete/whole, the universe is full/complete/whole. God is the efficient and material cause of the universe, which is created from Him and returns to Him. this act of creation and dissolution doesnt diminish Gods fullness.

for monists, both the universe and God being described as full means that the universe is God. for dualists, it means both God and the universe have an essence which is complete.