The ibtilaa' (testing) of the believer is like medicine for him. It cures him from illness. Had the illness remained it would destroy him or diminish his reward and level (in the hereafter). The tests and the trials extract these illnesses from him and prepare him for the perfect reward and the highest of degrees (in the life to come).
Ibn Qayyim Al-JawziyyaFrom the perfection of Allah's ihsan is that He allows His slave to taste the bitterness of the break before the sweetness of the mend. So He does not break his believing slave, except to mend him. And He does not withhold from him, except to give him. And He does not test him (with hardship), except to cure him.
Ibn Qayyim Al-JawziyyaThere is no joy for the one who does not bear sadness, there is no sweetness for the one who does not have patience, there is no delight for the one who does not suffer, and there is no relaxation for the one who does not endure fatigue.
Ibn Qayyim Al-JawziyyaAnd verily for everything that a slave loses there is a substitute, but the one who loses Allah will never find anything to replace Him.
Ibn Qayyim Al-JawziyyaThe heart becomes sick, as the body becomes sick, and its remedy is al-Tawbah (repentance) and protection [from transgression]. It becomes rusty as a mirror becomes rusty, and its clarity is obtained by remembrance. It becomes naked as the body becomes naked, and its beautification is al-Taqwa. It becomes hungry and thirsty as the body becomes hungry, and its food and drink are knowledge, love, dependence, repentance and servitude.
Ibn Qayyim Al-Jawziyya