God allows His saints to be tried by every sorrow, then to experience anew and prove His aid, and to understand how great a providence He has for them, for in their perils He is found to be their Redeemer.
[...] If a man is not first tried by the experience of evils, he has no taste for the good. Hence when in evils he meets with that which is good, he will be unable in knowledge and freedom to make use of it as being his very own.
How sweet is knowledge that is gained from actual experience and diligent training, and what power it gives to the man who through much experience has found it within himself, the same is known by those who have been assured of and have seen the help it affords them.
Then they learn the weakness of their nature and the help of Divine power, when God first withholds His power from them while they are amid temptations.
Thus He makes them conscious of their nature’s impotence, the arduousness of temptations, and the cunning of the enemy.
Thus he gives them to understand against whom they must wrestle, what kind of nature they are clothed with, how they are protected by divine power, how far they have advanced on the way, to what height God’s power has raised them up, and how powerless they are before the face of every passion when the divine power is withdrawn from them.
Through all these things they acquire humility, cleave closely to God, look for His help with expectation, and persevere in prayer.
[...] The diligent are tried, that they might add to their riches, the lax are tried, that they might guard themselves from what is harmful; the sleepy are tried, that they might be armed with wakefulness, those afar off are tried, that they might draw nearer to God; those who are God’s own are tried, that with boldness they might enter into His house.
The son who is not trained will receive no profit from the riches of his father’s house. For this reason, then, God first tries and afflicts, and thereafter reveals His gift. Glory to our Master Jesus Christ Who brings us the sweetness of health by stringent medicines!
There is no man who will not feel oppressed at the time of training, nor any who will not find the time bitter wherein he is given the medicine of trails to drink. Without temptations a man cannot acquire a strong constitution, yet to endure with patience is not within our power.
For how should the clay vessel endure the vehemence of the waters, if the divine fire had not hardened it?
Isaac the Syrian (c. 630-c. 700): Homily 61; longer text @ Kandylaki.