geongangi jungyohaeyo.

The 이 here is the subject particle:
• Nouns ending in a consonant take 이 as the subject marker.
• If 건강 ended in a vowel, you’d use 가 (e.g. 아이 → 아이가).

중요해요 is the polite present form of the descriptive verb (형용사) 중요하다 (“to be important”). In Korean:
• Descriptive verbs end in -다 in the dictionary form.
• They behave like verbs in conjugation but carry adjectival meaning.

1. Drop the dictionary ending -다: 중요하-
2. Change 하 to 해 (regular 하-verb change)
3. Add the polite ending -요
   Result: 중요하
   • 해
     • 요 = 중요해요

• The -요 ending (해요체) is polite/casual speech used in everyday conversation with strangers or acquaintances.
• -습니다 ending (합니다체) is more formal/polite and often used in presentations, news broadcasts, or when speaking to superiors.
So 건강이 중요합니다 is the formal equivalent.

• 건강이 중요해요 uses the subject marker 이, simply stating “Health is important.”
• 건강은 중요해요 uses the topic marker 은, which can imply contrast or emphasis (e.g. “As for health, it’s important, but …”).

• Past: 건강이 중요했어요 (“Health was important”)
 – 중요해요 → stem 중요하- + 었 + 어요
• Future: 건강이 중요할 거예요 (“Health will be important”)
 – use modifier 중요할 + 거예요

You can add adverbs before 중요해요:
• 정말 중요해요 – “really important”
• 매우 중요해요 – “very important”
• 아주 중요해요 – “quite/very important”