Multiplication has far reaching spiritual implications over the physical. This is indeed the first commandment given to man and it happens on the onset of the 7th day. It's curious why the 4th commandment seems to be set at the highest level citing the 7th day of creation as its authentication. There is no commandment on the 7th day but there is a commandment that predates the 7th day and that is the commandment of multiplication.
The 7th day of creation is ushered in upon the completion of the work of creation. God does not "rest" he ceases his work, and he ceases because his work is complete. Rest cannot happen when the work is not complete. This is why the 7th day contrasts before the first day of light/darkness, complete/incomplete, formed/unformed, rest/chaos, etc... the 7th day is tantamount to completion and before light is spoken is the antithesis of the 7th day.
Christ says in John 5:17 "My Father is always at his work to this very day, and I too am working" Christ's work is the multiplication of his kingdom. It is a spiritual multiplication. We may partner with Christ in this labour and when complete it will user in the 7th day. We are charged with this since the beginning, echoed in the law, the NT such as in the great commission, or places like the opening of Acts.
Until the work is complete any rest we take is a false rest.