Two

When two things are closely associated, they represent one thing which has two aspects. Sometimes the one thing is hard to name.

One thing	heavenly/spirit	earthy/flesh
creation	heaven	earth	Ge 1:1
nature of existence	without form/vain	void	Ge 1:2
nature of God	light/holiness/Day	dark/love/Night	Ge 1:3
relationship	evening/separation	morning/reconciliation	Ge 1:5
waters/word	waters above	waters below	Ge 1:6
waters below/	seas/chosen	dry land/desolate	Ge 1:10

Repetition

When the same phrase is used twice, it means that it is true in a fleshly and a spiritual aspect.

Le 1:3 'he shall bring near him' is repeated. It is translated that 'he shall voluntarily bring near him'. Not only must he physically bring it, but he must willingly bring it.