What is the wisdom behind the impermissibility of outright lying when necessary, such as to cover for people or to ward off a great harm, and is it necessary to use allusions (ta'ridh), and how should a Muslim act if they cannot find a phrase for allusion?

Concealing people's faults and warding off harm from them is necessary, and the use of allusions (ma'areedh) should be employed whenever possible. If that is not possible, then there is no sin in lying. Every praiseworthy objective that cannot be achieved except through lying is permissible if the objective itself is permissible, and it is obligatory if the objective is obligatory.