John Nelson Darby addresses the struggle with unbidden and hated evil thoughts that arise even when one is focused on the Lord. He emphasizes the need for deliverance from the flesh and encourages believers to recognize that these thoughts do not define them. Instead of stopping to confess these thoughts, Darby advises to ignore them and continue in communion with God, as acknowledging them only gives power to the flesh. He reassures that this experience is common among believers and encourages a focus on God's strength in moments of weakness.

(Extract from a Letter.) {Pamphlet published by Morrish} Dear -, I have your letter, and I am sure that the enemy is very busy, as well as the evil heart within. What you need is thorough deliverance from yourself, that is, the flesh. You speak of evil thoughts, unbidden and hated, springing up in the heart even when you seek to be occupied with the Lord, this too when really thinking of Him. Then you stop to confess them, and the occupation for a moment in confession only provokes another evil thought. And so it is as you say, an unending, all-day work. My feeling is that you have never yet enjoyed full deliverance from self and flesh. You are what scripture calls still "in the flesh," though a believer in the Lord Jesus Christ. I believe if your soul were free you would find the simple yet profound truth of "reckoning yourself dead" (Rom. 6:2), would so act that the thought of turning aside to confess what would spring up unsought for in your soul, would be found to be really and only allowing the flesh a triumph, in leading you to be occupied with it. When there is no will, such thoughts will be left, turned aside from, and treated as "not I." Of course when the soul is not free I could not say you could do so at all, but were freedom enjoyed you would not be the sufferer from such things. What I would simply say to you is, when evil thoughts are present to your soul, unsought for and hated, do not stop or cease from your measure of occupation with the Lord, to confess them. If will enters they must be confessed, but if not pass them by as you would avoid an evil person who is not yourself, and who you know is incorrigible, and with whom contact is only misery and defilement. "Avoid such, pass not by them," but leave them there. To own them at all, is but to give the flesh the place it seeks - a recognition in some way or another. This, even when it is only to abhor its workings, will be a satisfaction to the flesh. Oh that you had grace to leave "the flesh" unrecognised and disowned, and to pass on conscious that it is always there and will be in you to the end. How blessed that we can by grace disown and refuse to hear its suggestions when it works, knowing through mercy that it is no more "I." Your case is one that has been and is common to most of the Lord's people, if not all. I refer to unsolicited, hated and wandering thoughts. You should simply go on and take no notice of them whatever, as by doing so you only give the flesh the place it seeks. Go on as not hearing the suggestions - be as it were deaf to them. Confess to God if you find will at work, but not so as to be occupied with the analysis of the evil: rather look up to Him, the sense of weakness and impotency filling your heart, and in the attitude of dependence of soul, pass on with your eye resting on Him, out of whom strength comes whenever there is conscious weakness.