"The Cell is the fundamental building block of life." as the cell are the smallest part of the body and perhaps makes other things,like the basic thing for a building is brick.As we all know first the body has cells then tissues then organs then organ systems and the a complete body.
Hence the meaning of 
"The Cell is the fundamental building block of life." is clear
 We should always keep this in mind that all the substances are made up of atoms. In case of living cells these atoms have combined to make up various molecules which have combined to form various organelles and ultimately cells. But in non living substances this interaction between atoms and molecules has not taken place and hence they are lifeless. Any thing below the cellular level of organisation is non living and does not show characters shown by living organisms. Take the example of viruses which are non living till the time it does not acquire a cellular machinery. This is the reason why cell is the fundamental building block of life.
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