[von_lohengramm]

That does not describe all Forths. A Forth running on a Forth CPU would certainly be a 2nd level, but depending on how the Forth is implemented and designed, it could easily be seen as a 3rd level. Arguably, Forth is (can be) more abstract than C and almost a quasi-FP.

[drran]

It's possible to implement high-level abstraction in machine code, or compile a high-level language into low level machine code, however it's not possible to hide low-level, machine dependent details in a low level language. It's not possible to hide machine opcodes in machine code, or CPU registers in assembler, or stack in Forth, so a developer must learn these things and deal with them, which makes the development process slower.

So, it's expected to see an order of magnitude improvement in development speed, on average, when jumping from machine code to asm, or from asm to a 3rd level language. Forth doesn't improve speed of development by an order of magnitude comparing to asm, because of the steep learning curve and low level stack management. I tried to learn Forth multiple times, but still cannot program in Forth freely, which makes it unique among 20+ other programming languages I know.

[lebuffon]

IMHO Forth has a longer learning curve than other languages and requires a significant mental model shift if you are use to conventional languages. It does not suit everyone. It seems more like learning a new human language with a large number of words.

Chuck Moore created Forth to improves his productivity versus conventional tools and there is some anecdotal evidence that it worked for him and those that worked with him, particularly where direct hardware control on new hardware could be interrogated and validated via the interpreter rather than an Edit/Assemble/Link/Test loop.