Oh he's a sneaky one ... but a good part of the battle is won just by knowing his tactics.
The devil hates to see us progress along the path of virtue. When we grow in holiness, instead of shrinking away, the devil will double his efforts and try to use our virtue to turn us towards vice.
Italian priest Fr. Lorenzo Scupoli writes about the strategy of the devil in this circumstance in his spiritual classic, The Spiritual Combat, published in 1589. He explains how the devil will do one of two things.
First of all, the devil will try to tempt us with good works that are beyond our capacity. This can create within us a sense of disappointment, tempting us to return to our life of sin, and give up our struggle because we can never be perfect.
Scupoli gives the example of a person suffering from an illness, desiring to do good that is out of his reach.
A sick person is perhaps bearing his illness with a patient will. The cunning adversary knows that by this means he may attain to a habit of patience; and he immediately sets before him all the good works which in a different condition he might be able to perform, and tries to persuade him that if he were but well he would be able to serve God better, and be more useful to himself and others.
Having once aroused such wishes within him, he goes on increasing them by degrees, till he makes him restless at the impossibility of carrying them into effect; and the deeper and stronger such wishes become, the more does this restlessness increase.
The key to resisting Satan’s cunning is to trust in God, focusing on our current situation, being satisfied with what we can do in the present moment. Instead of being dissatisfied with what “could be,” it’s better to remain rooted in the here and now. God will take care of the rest.
Secondly, the devil can use our virtues as a cause for pride. He can tempt us into thinking that we are the sole cause of our virtue, or that we are better than others. This can easily lead us down the wrong path.
The cunning and malicious serpent fails not to tempt us by his artifices even by means of the very virtues we have acquired, that, leading us to regard them and ourselves with complacency, they may become our ruin; exalting us on high, that we may fall into the sin of pride and vainglory.
To preserve yourself from this danger, choose for your battlefield the safe and level ground of a true and deep conviction of your own nothingness, that you are nothing, that you know nothing, that you can do nothing [without God].
We must always remember that even when we make progress in the spiritual life, it has nothing to do with us, but everything to do with God.
Above all, be vigilant! If you want to progress in virtue, be aware that the devil will use our good desires and try to turn us away from God.