In the Standard Model (and all theories extending it), the fundamental interactions are based on symmetry principles (gauge symmetries). This works super well and reproduce tons of data. However, those symmetries forbid the particles to be massive. One way out is to use spontaneous symmetry breaking (which was proved to work with the discovery of the Higgs boson that consists in a left-over of this mechanism). This allows to keep the symmetries and generate masses for all the particles.

For more information, feel free to have a look in this post, and to come back to me with any further question. I will be glad to answer them.