The layout of a machine instruction is part of the architecture of a processor chip. Without knowing the layout you can't tell what the instruction means. Even if you know the layout, it is hard to remember what the patterns mean and hard to write machine instructions.
A statement in pure assembly language corresponds to one machine instruction. Assembly language is much easier to write than machine language. Here is the previous machine instruction and the assembly language that it corresponds to:
machine instruction assembly language statement 0000 0001 0010 1011 1000 0000 0010 0000 add $t0,$t1,$t2
The instruction means: add the integers in registers
and put the result in register
To create the machine instruction from the assembly language
statement a translation program called an assembler is used.
Humans find assembly language much easier to use than machine language for many reasons.
Enhanced assembly language includes additional convenience features. It has instructions (called pseudoinstructions) that correspond to several machine instructions.
Once you know assembly language, is it hard to write an assembly language statement?