I think there comes a point in every person’s life in which they feel they cannot keep fighting the same sin over and over. Recently, a young man admitted that he was thinking about quitting church due to his addiction to pornography and being too embarrassed to keep confessing his sin every week to the same priest. Such a story is not uncommon.
In the spiritual struggle, one of the devil’s most successful tactics is to convince people that resistance will inevitably fail. As I wrote in The Warrior’s Heart, we must not ever give up. Our struggle is the most important aspect of the battle with the passions; even more so than victory.
To those who feel hopeless, St. Isaac the Syrian writes,
Whenever a man falls, he should not forget the love of his Father. And if it happens that he fall into manifold transgressions, he should not be negligent concerning the good, nor should he stop his onward course, but even though he was vanquished, he should rise up again to struggle against his adversaries and each day begin to lay a foundation for his ruined dwelling, having the words of the Prophet in his mouth until his departure from this world, “Rejoice not against me, mine enemy, that I have fallen; for I will rise again; for though I should sit in darkness, the Lord shall be a light unto me.” (Micah 7:8)
May he never cease from making war until his death, and as long as there is breath in his nostrils may he not surrender his soul to defeat, even at the very moment of his defeat! 
CALEB: OLD BUT NEVER RETREATING
It reminds me of the story of Caleb in the books of Numbers and Joshua. When nearly all of Israel ran from the Promised Land, afraid to war with the Philistines, Caleb did not lose heart, but had a warrior’s spirit. It says of him,
But My servant Caleb…has a different spirit in him and has followed Me fully… (Numbers 14:24)
Forty-five years pass before Israel is given another shot at the Promised Land. Caleb is eighty-five years old and yet he boldly proclaims,
Here I am this day, eighty-five years old… just as my strength was then, so now is my strength for war, both for going out and for coming in. Now therefore, give me this mountain [filled with fortified enemy cities]. It may be that the Lord will be with me, and I shall be able to drive them out as the Lord said. (Joshua 14)
This too should be our attitude toward temptations and difficulties. Caleb has no way of absolutely knowing that he, as an eighty-five year old man, will be victorious in battle. Yet he looks upon a mountain filled with heavily defended cities, and says, “Give me that mountain!” We should look upon the mountains that are our sinful habits and difficulties, and say unto God, “Give me that mountain!”
Later, St. Isaac quotes St. Martinian,
Persevere… and you will achieve that thing most desirable and praiseworthy, to prove steadfast and unmoving in war, reddened by the blood of your wounds. Never cease, therefore, from wrestling with your adversaries. 
I pray that God will grant all of us spiritual valor so that we may say, “Should I somehow end up in hell, I hope that I have at least given Satan a good beating on the way down!”
Rather than become despondent or hopeless when we are defeated, we should rise up one more time; always one more time. I do not believe God will cast anyone into hell because they struggled with temptations — as long as they kept fighting. When writing about the multitudinous afflictions and hardships that we face as Christians, St. Paul writes,
Yet in all these things we are more than conquerors through Him who loved us. For I am persuaded that neither death nor life, nor angels nor principalities nor powers, nor things present nor things to come, nor height nor depth, nor any other created thing, shall be able to separate us from the love of God which is in Christ Jesus our Lord. (Romans 8:37-39)
Some of the blogs I’ve written on this topic:
Books on this topic:
- Spiritual Struggle (St. Paisios of Mt Athos)
- The Arena (St. Ignatius Brianchaninov) .
- Unseen Warfare (St. Nicodemus of the Holy Mountain)
- The Ascetical Homilies of St. Isaac the Syrian (St. Isaac)
 The Ascetical Homilies of St. Isaac the Syrian, Homily Nine, pg. 190-191. Holy Transfiguration Monastery, 2011.
Main image is from either a French or English illuminated manuscript produced in the mid 1400’s. It is St. Michael slaying the dragon. From the Getty Research Institute.