“私は” (watashi wa): “I” or “me” with the topic marker “wa”. This sets up what the rest of the sentence will be about, i.e., it’s about what “I” did.
“自分のために” (jibun no tame ni): “for myself”. The word “jibun” means oneself, “no” is a possessive particle (of), and “tame ni” translates to “for the benefit of” or “in order to”. So together, it means “for my own benefit” or “for myself”.
“そうしたのです” (soushita nodesu): This is a past tense verb followed by “nodesu”. The verb “soushita” is the past form of “sousuru”, which means “to do so” or “to do that”, referring back to something previously mentioned or understood from context. The “nodesu” is a phrase that adds explanatory tone to the sentence, often translating as “it is that…”, or simply used to give or ask for explanations.
So, all together, “私は自分のためにそうしたのです。” would translate to “I did it for myself.” The “nodesu” suggests that this sentence is explaining the reason or purpose for the speaker’s actions. It might be used in response to a question or a situation where the speaker feels the need to justify or explain their actions.