• 八(eight (pictographic, two strokes separating))

Two strokes separated apart like two objects dividing represent the number eight.

• 八(divide; separate; eight)
• 刀(knife; blade; sword)

Using a knife to chop something in half represents division or separation.

• 之(walk; arrive; step on ground)

A footstep moving forward on the ground represents "go to," which then becomes a grammatical particle.

• 一(first; number one (pictographic))

A single horizontal stroke symbolizes the number one, the beginning of all things.