이것을 사물의 변화라고 합니다.1 This is called the transformation of things.
이것 is a compound word formed from 이, a demonstrative determiner meaning ‘this’, and 것, a bound noun meaning ‘thing’, together meaning ‘this’ or ‘this thing’.
을 is an object marker that identifies the noun as the target directly affected by an action.
이게 내가 택한 자유니까2 Because this is the freedom I chose.
이게 is a contraction of 이것이, where 이 is a demonstrative determiner meaning ‘this’, 것 is a bound noun meaning ‘thing’, and 이 is a subject marker that identifies the noun as the entity that performs an action or is in a particular state.