To understand what it means, let's unpack the text of the decision.
Sufficient justification for the purpose and circumstances of the intended stay was not provided.
That's one of the standard reasons for refusals provided in the Schengen Visa Code and other official documents. In general, it means that the consulate is not convinced you have a valid purpose for travel. There are many reasons why that might be and the rest is just an explanation of how they reached that conclusion.
The specific purpose for which the visa was applied for is no longer valid or will cease to be valid before you arrive in the member state of destination.
This one is more specific and should help understand the first one. What this means is that the purpose for the trip you described in your original application might have been valid at some point in the past but it is not current anymore. Imagine you want to attend a conference but your application is delayed and the date of the conference has passed by the time the application is being assessed. Going to a conference is a perfectly valid purpose for a trip but if that specific conference has passed, you cannot possibly attend it and it's not a valid purpose for a visit anymore.
It's difficult to say more without knowing more about your application but there are currently many restrictions on entry, travel and access to public areas across Europe due to the Covid-19 pandemic. So there are many legitimate trips to the Schengen area that are just not possible anymore. For example, if you applied for a visa to vacation in Italy, providing hotel bookings, etc. your trip does not have a purpose anymore as it won't be possible for you to stay at these hotels or visit any sights.
No other (secondary) purpose was stated at the time of the application, [or] if it was, insufficient documentation was provided to demonstrate the purpose of the stay.
A single journey can very well have several purposes. Even if one of them ceases to be valid, it doesn't mean that the trip is necessarily useless. But, in the judgment of the consular officer, you did not describe any other sufficient purpose for this journey. It could be a reference to some detail of your application or simply some boilerplate they add to all such decisions.
[Note: I changed “of“ into “or”. It makes more sense in this sentence; it could be a simple typo or a confusion with the Dutch word “of“, which does mean “or”.]
So what does it mean for you? The decision is negative, you won't get a visa and cannot travel at this time. An appeal does not seem to make sense to me so you will need to start a new application from scratch if you want to travel to the Schengen area in the future.
On the other hand, that's not the worst reason to be refused a visa. Nothing suggests the consular officer suspected that you might be lying (they can use a different phrasing - “the justification […] was not reliable” in that case) and they haven't expressed any doubt regarding your personal situation and willingness to abide by the rules. So a new application in a few months from now, when Covid-19 restrictions have been lifted, seems like it would have good chances to be successful.