so for any morphism $f:C \to C'$ we have a commutative diagramm $$\require{AMScd} \begin{CD}
\operatorname{Hom}(C',A) @>{i_{C'}}>> \operatorname{Hom}(C',A')\\ @V{\operatorname{Hom}(f,A)}VV @V{\operatorname{Hom}(f,A')}VV\\
\operatorname{Hom}(C,A) @>>{i_C}> \operatorname{Hom}(C,A')
\end{CD}$$