What does 子曰, 三十而立, 四十而不惑 mean?

Most of the time it is easier for me to translate Literary Chinese by thinking in English, but sometimes it is easier to translate it by thinking in Korean. Here is an example of a sentence that is easier for me to understand by thinking in Korean:

Example Sentence:

子(자)曰(왈), 三(삼)十(십)而(이)立(립), 四(사)十(십)而(이)不(불)惑(혹).

Vocabulary:

• 子 -- "Master," Confucius; 공자 (孔子)
• 曰 -- to say (used when quoting someone)
• 三 -- three
• 四 -- four
• 十 -- ten
• 而 -- and; then; 에
• 立 -- established; independent; 자립 (自立)
• 不 -- not; no
• 惑 -- doubt; 의혹 (疑惑); 미혹 (迷惑)

Translation:

The Master (子) said (曰), “At thirty (三十而), [I] was established [in society] (立).  At forty (四十而), [I was] without (不) doubts (惑).”

Notes:

In English, 而 could be translated as "and" or "then," resulting in translations like "30 and established; 40 and without doubts" or "30, then established; 40, then without doubts." However, for me it is easier to first mentally translate this sentence into Korean, resulting in 삼십에 (三十而) 자립 (立); 사십에 (四十而) 불혹 (不惑), which I then translate into English as "At 30 [I] was established; at 40 [I] was without doubts," The phrase "without doubts" means "confident." "In Korean 而 translates as 에, which translates in English as "at." When I see a number or a time word like 二月 followed by 而, I first think of 에.