to try them - the design of affliction. Image from metals tried with fire.
to purge - Even in the elect there are dregs which need to be purged out (1Pe 1:7). Hence they are allowed to fall for a time; not finally (2Ch 32:31; Luk 22:31). Image from wheat cleared of its chaff by the wind.
make ... white - image from cloth (Rev 7:9).
to ... time of ... end - God will not suffer His people to be persecuted without limitation (1Co 10:13). The godly are to wait patiently for “the end” of “the time” of trial; “for it is (to last) yet for a time appointed” by God.