Yes, it may look a little familiar because Afrikaans and English are both Germanic languages.
Opstanding is historically built from elements meaning something like standing up / rising up:
But in normal usage, opstanding means resurrection, not just standing up in an ordinary physical sense.
In this sentence, belangrik comes after is, so it is being used predicatively: it describes the subject after a linking verb.
In Afrikaans, adjectives used this way usually do not change form:
So belangrik stays the same.
Usually, Die opstanding is belangrik sounds more natural if you mean the resurrection as a specific concept or event.
Leaving out the article can sometimes happen in special styles, headings, or very general statements, but in ordinary standard prose this sentence is most naturally said with die.
So for a learner, the safest version is:
A rough English-friendly guide would be:
A few tips:
These guides are only approximate, but they are enough to help you start recognizing the words.