There is no doubted to this and on that context of  discussion when I come across it, I don't hesitate that "of we don't buy now, will tomorrow be too late"? Which I know that there no ever late entry in the bitcoin market but what has to be considered is "are we determined to hodl? Because even those who bought bitcoin in the earlier days when it was launched had to also hodl and til then is how the market price keep improving.
The phrase "but now" really sounds somehow like some persuasive words which can even convince newbies or enthusiasts to rush into buying like the phase of the market has been predicted to surge in the moment while leaves others into panic to buy at their unplanned time.

I think you took the phrase "Buy bitcoin now" out of context. The advice that one should buy bitcoin now doesn't mean they shouldn't study about bitcoin before buying. It also doesn't mean they shouldn't study how to safe-keep their bitcoin before buying. But is is only point to one direction and that is for procrastinator. Those who will keep postponing their plans of buying bitcoin because of price volatility. They will be like, I will buy when the price falls to $30k. So, the "Buy bitcoin now" phase is just like a call to action to tell them that no time is too bad to buy bitcoin and now is the best time.

Mostly those who want to invest huge money in Bitcoin are the ones who care so much about the security, privacy and protection of their coins but for those lower investors, they don't care much about the security of their assets because of the mindset that they don't own enough Bitcoins. The security of anything that concerns money should be taking seriously because every amount is valuable so far as Bitcoin is concerned. The little amount we invest today can turn out to be a big investment tomorrow. Truly, due to Internet scams and frauds, many people want to have a basic knowledge about Bitcoin before investing which is not bad at all. The statement 'buy Bitcoin now' is just a phrase used to motivate people to buy Bitcoin despite the high price because its potential in the future will be worth it

Yes I am trying to understand the link the OP makes between buying Bitcoin now
and security and being aware of scams.

Everyone knows or should know the best time to buy Bitcoin is now, particularly
if you have no intention to be a trader and you have a long term outlook.

Also everyone needs to keep up to date as much as possible with scams and
scam sites. So we need to be aware of getting scammed regardless of
where, how or when we buy Bitcoin, it should go without saying.

What I understand from that statement is that if you have the capital, there is no point in procrastinating further; the best time to invest is now because you don't know what tomorrow holds.

I don't think that phrase is intended to mount pressure on anyone, it's just trying to let those who have all it takes to invest stop procrastinating. Ordinarily, anyone with common sense should know that buying Bitcoin also involves knowing what you are buying and why you are buying it. Once anyone begins to pressure you, you should pause and have a rethink. It is only careless people that will succumb to such pressure without thinking twice.

Of course the most important thing is security, there is no point in investing if you are not in a safe environment or if you are not informed about something. It will not gain you anything. So the best time to buy bitcoin is when you know what you are buying and you feel safe.

If not, of course, it's always the best time to buy bitcoin, the price you buy today may be higher than the price tomorrow, but you will definitely be buying it at a much cheaper price than a few years from now

"Buy Bitcoin now" is not a phrase that suggests that you must buy Bitcoin immediately or it is a necessity that you must own Bitcoin, it simply suggests that Bitcoin is profitable. I assume that the phrase doesn't undermine the importance of gaining Bitcoin knowledge before you buy, it just depends on how somebody interprets the meaning. Anybody that wants to invest their money in a business or project without gaining knowledge is simply gambling their funds, you need to understand how Bitcoin works and how to protect your wallet from hacks and scams. Thankfully there are materials online to guide newbies about Bitcoin investment.

Protection of you assets at all times is always very key and as stated by OP I agree to that, this doesn't mean you have to wait till you get a complete knowledge of Bitcoin or crypto assets generally before you  begin to buy, the fight against fraudulent practice around  the crypto space is no news and to a very great extent a good percentage of people in the crypto space are very much aware of this, one good thing  about this space is that the issue of security personally is very simple such that all you have to do is abide by it and you  will be safe.

As a newbie just  get these basic knowledge of knowing how to use a wallet, how to protect you seed phrase and not storing your assets on exchanges and you are good to go. Provided you are using a safe wallet of which by recommendation from reputable people you will get that sorted, you can be sure of your safety at least to a 80% benchmark because honestly no 100% guarantee of safety actually.  So you don't need to be a cyber security expert before you start investing, if you are waiting for such bulk of knowledge to protect your assets before you begin to invest, you may get in on a higher price than you would have if you had started earlier understanding only the basics which is almost literally all that's needed for you to know before investing.

In my opinion saying the best time to buy is now sounds good in theory but without the right knowledge it can be risky. It's not just about buying bitcoin anymore it's about knowing how to store it protect it and understand what you're getting into. Education should come before any investment decision in this space