Ambrose (340-397) writes:
Often we hear talk about fleeing from this world, and I wish that the mind were as careful and circumspect as talk is easy! But, what is worse, the allurement of earthly lusts frequently creeps in, and influx of vanities takes over the mind, so that what you endeavour to avoid, you think about and turn over in your mind. It is difficult for a man to guard against this, but impossible for him to get rid of it. Indeed, in this matter the wish exceeds the accomplishment, as it attested in these words of the prophet: “Incline my heart unto your testimonies and not to covetousness.” For our heart is not within out own power, nor our thoughts, which, poured out unexpectedly, swamp the mind and soul, and draw you in a different direction from that which you have proposed. They recall us to temporal things, they introduce worldly concerns, they suggest pleasures, they weave enticements, and in the very time when we are preparing to elevate our minds, we are usually enveloped with vain thoughts and cast down to earthly things.
What is your gut reaction when you read that? Mine is this: It rests not in our power to be holy, but in God’s. We receive this from Him who inspires our heart, who brings about life where there was no life, the one who turns the heart of stone into the heart of flesh. No matter how hard I try I can’t change my behaviour and thoughts, my heart is wicked. I see my depravity come through in so many ways during the day and this leads me to rest in Jesus more. After all, He calls us to himself to be holy, to be set apart. We aren’t to be holy so we can walk up and down the street flashing our holy badge, instead we are called to be holy to reflect His glory in all that we do.
If you are seeking true change in your life, you must stop trying to do everything by your own power and turn to Jesus and rest in His.
But by the grace of God I am what I am, and his grace toward me was not in vain. On the contrary, I worked harder than any of them, though it was not I, but the grace of God that is with me. – 1 Corinthians 15:10