In addition to that, the emotion unleashed with a form of communication like symbolism grips our souls strongly, since man is ultimately a being
of emotion in all matters of life. Imagine how drab it would be if our Christ simply said, when he was condemning the Jewish elites in their synagogue;
>You bad people who are influenced by Satan and who are also quite deceitful!
instead of
>You brood of vipers!
One provides a description quite like the analogy, yet it lacks such an emotive tone of describing these vicious people, whom, keep in mind, in this particular instance, have even gone as far as to deny The Holy Spirit. Meanwhile, the alternative gives us a clear comparison to a familiar creature--of this terrible, conniving wickedness that inhabits the essence of the viper--all while holding within itself a visible emotion of pained denouncement that Christ expresses for those who he's speaking to. From an example like this, you can see that one is often more effective than the other in conveying a point