Solar flares and eruptive events are driven by the 3D evolution of current-carrying magnetic fields in the solar atmosphere. While several mechanisms have been identified, we still do not know which ones are really responsible for the trigger of these flaring phenomena. This is because our knowledge of the 3D magnetic field in the solar atmosphere mostly rely on the approximate 3D solution obtained from force-free coronal magnetic field extrapolations of the 2D photospheric measurements. The European Solar Telescope will provide magnetic field measurements of the solar photosphere and chromosphere with unprecedented polarimetric sensitivity and very high spatial and temporal resolution. Such measurements will provide original information for better constraining the 3D magnetic field in the solar atmosphere. In this talk, we discuss how EST measurements may help us identifying the mechanisms triggering solar flares and eruptive events, and the relationships between the local 3D magnetic field properties and the flare signatures.