Why does the cell need to carry out transcription before it can begin translation

The cell needs to carry out transcription before it can begin translation because transcription is the first step of gene expression, whereby the segments of DNA is copied into RNA in other words mRNA by enzymes RNA polymerase.
 Both RNA and DNA are nucleic acids and they use base pairs of nucleotides as complementary language. It is during transcription when DNA sequence is read by an RNA polymerase which produces antiparallel RNA, complementary strand called primary transcript.
Transcription unit is the stretch of DNA which is transcribed into an RNA molecule and it encodes a protein then the transcription produces messenger RNA or mRNA the mRNA serves as a template for synthesis of proteins through the process of translation.
The transcribed gene may encode for either ribosomal RNA or rRNA, non-coding RNA for example microRNA. RNA performs a fundamental role in functions within a cell whereby it helps to regulate, synthesize, and process proteins.

When a virus infects a host cell, it uses the cell's machinery to make copies of its own genetic material in a process called replication. finally, during the process of self-assembly, that protein shell and the copies of the virus's genetic material are assembled into new viruses.