It comes from his 8-volume collection of sermons on the book of Ephesians. In his volume The Christian Warfare he expounds upon Eph. 6:10-13. And this quote comes from chapter 8, "Heresies," (found on pp. 108-120). In it he is commenting on a portion of Eph. 6:11: "Put on the whole armour of God, that you may be able to stand against the wiles of the devil."

Needless to say, the entire chapter is important reading, but let me offer portions of it here. He begins by noting how we err in underestimating the reality of a personal devil. This malevolent being is not just some vague and generic 'principle of evil.' Instead, says Lloyd-Jones:

A principle cannot be subtle. It is only a person who can be subtle. 'The wiles of the devil!' The Apostle's whole object is to tell us that we are not fighting merely against flesh and blood, merely against some principle, or absence of principle, which is within us as flesh and blood, as men and women. He goes out of his way to say that it is quite otherwise. In other words what he says is the exact opposite of what is being taught commonly at the present time.

He continues in this vein for a bit, saying this "digression is important," and then he goes on to look at some of the strategies of the devil. One general strategy is for people to flee from reality and eschew the "negative". He says that many folks during the last great war who just "wanted to be happy and to enjoy themselves, and dismissed the man who kept on warning us as a 'warmonger', a 'difficult person' with whom nobody could work..." He then says:
Precisely the same, it seems to me, is happening in the realm of the spiritual today. People say, 'Do not be negative; let us be positive; let us just preach the simple gospel'. But the Bible is full of negatives, full of warnings, ever showing us these terrible possibilities. If you find in yourself a dislike of the warnings of the Scripture and of this negative teaching, it is obvious that you have been duped by the wiles of the devil. You have not realized the situation in which you are placed.

He then gets to the issue of heresy. He goes into some detail here and is worth quoting at length. Says Lloyd-Jones:
A heresy is 'a denial of or a doubt concerning any defined, established Christian doctrine'. There is a difference between heresy and apostasy. Apostasy means 'a departure from the Christian truth'. It may be a total renunciation or denial of it, or it may be a misrepresentation of it to such an extent that it becomes a denial of the whole truth. But a heresy is more limited in its scope. To be guilty of heresy, and to be a heretic, means that in the main you hold to the doctrines of the Christian faith, but that you tend to go wrong on some particular doctrine or aspect of the faith.

The New Testament itself shows us clearly that this tendency to heresy had already begun even in the days of the early Church. Have you not noticed in the New Testament Epistles the frequent references to these things? There is scarcely one of them that does not include mention of some particular heresy that was creeping in, and tending to threaten the life of some particular church. It is seen in this Epistle to the Ephesians; it is still more plain, perhaps, in the Epistle to the Colossians where heretical tendencies were entering through philosophy and other agencies. It is found likewise in the Epistles to Timothy.

Incipient heresy can be detected from the very earliest days. There is an enemy who comes and sows tares. I am not applying that parable in detail, I am using it as an illustration to show the kind of thing we are considering. The enemy's object, of course, is to disturb the life of the Church, to shake the confidence of Christian people, to spoil God's work in Christ. The Epistles were in a sense written to counteract these evils. The threat was already there in many different forms, for before the New Testament closes, all the major heresies were beginning to show their heads in the Early Church.

But from the second century of the Christian era the evil becomes still more evident and obvious. The simple fact is that for several centuries the Christian Church was literally fighting for her very life. With the conversion, and the coming in, of those who were trained in Greek philosophy and teaching, all kinds of dangers immediately arose, and the danger became so great as to threaten the whole life of the Church.

People who called themselves Christians, and moved in the realm of the Church, began to propagate teachings that were denials of Christian truth. The threat became so great that the leaders of the Churches held certain great Councils in order to define the Christian faith. Their object was to pinpoint heresies, and to protect the people from believing them. Such confusion had come in that people did not know what was right and what was wrong. So the leaders met together in these great Councils, and promulgated their famous Creeds, such as The Athanasian Creed, The Nicene Creed, and The Apostles' Creed.

These Creeds were attempts on the part of the Church to define, and to lay down, what is true and what is not true. And in this way they were able to brand certain teachers as heretics, and to exclude them from the life of the Christian Church. The confusion that led to the drawing up of the Creeds was a great manifestation of the wiles of the devil. And today there are many people who recite these Creeds in their churches every Sunday, and then in conversation tell you that what you believe does not matter at all -- 'believe anything you like!' But the Creeds are a permanent reminder to us of the wiles of the devil in this respect.

He is aware that many believers today have little time for all this. But they ignore these matters at their own peril:
Is there someone who feels at this point, 'Well, really, what has all this to do with me? I am an ordinary person, I am a member of the Church and life is very difficult. What has all this to say to me?' Or there may be someone who is recovering after illness and who says 'Well, I was hoping to have a word of comfort, something to strengthen me along the way, something to make me feel a little happier; what has all this about Creeds and Confessions and the wiles of the devil to do with me?' If you feel like that, the truth is that the devil has defeated you. The Apostle Paul says, 'Be not deceived: evil communications corrupt good manners' (I Corinthians 15:33). He means that wrong teaching is desperately dangerous. He is there dealing with the great question of the resurrection, he is concerned with that one doctrine, and he says; Make no mistake about this; it is not a matter of indifference as to whether you believe in the literal physical resurrection or not. 'Ah but,' you say, 'I am a practical man of affairs, I am not interested in doctrine, I am not a theologian, I have no time for these things. All I want is something to help me to live my daily life.' But according to the Apostle you cannot divorce these things, 'Evil communications' --wrong teaching, wrong thinking, wrong belief -- 'corrupt good manners'. It will affect the whole of your life.

One of the first things you are to learn in this Christian life and warfare is that, if you go wrong in your doctrine, you will go wrong in all aspects of your life. You will probably go wrong in your practice and behaviour; and you will certainly go wrong in your experience. Why is it that people are defeated by the things that happen to them? Why is it that some people are completely cast down if they are taken ill, or if someone who is dear to them is taken ill? They were wonderful Christians when all was going well; the sun was shining, the family was well, everything was perfect, and you would have thought that they were the best Christians in the country. But suddenly there is an illness and they seem to be shattered, they do not know what to do or where to turn, and they begin to doubt God. They say, 'We were living the Christian life, and we were praying to God, and our lives had been committed to God; but look at what is happening. Why should this happen to us?' They begin to doubt God and all His gracious dealings with them. Do such people need 'a bit of comfort'? Do they need the church simply as a kind of soporific or tranquillizer? Do they only need something which will make them feel a little happier, and lift the burden a little while they are in the church?

Their real trouble is that they lack an understanding of the Christian faith. They have an utterly inadequate notion of what Christianity means. Their idea of Christianity was: 'Believe in Christ and you will never have another trouble or problem; God will bless you, nothing will ever go wrong with you'; whereas the Scripture itself teaches that 'through much tribulation we must enter into the kingdom of God' (Acts 14:22), or as the Apostle expresses it elsewhere, 'In nothing be terrified by your adversaries: which is to them an evident token of perdition, but to you of salvation, and that of God. For unto you it is given in the behalf of Christ, not only to believe on him, but also to suffer for his sake' (Philippians 1:28-29). Our Lord says, 'In the world ye shall have tribulation: but be of good cheer, I have overcome the world' (John 16:33). There is nothing which is so wrong, and so utterly false, as to fail to see the primary importance of true doctrine.

Looking back over my experience as a pastor for some thirty-four years, I can testify without the slightest hesitation that the people I have found most frequently in trouble in their spiritual experience have been those who have lacked understanding. You cannot divorce these things. You will go wrong in the realms of practical living and experience if you have not a true understanding....

Nothing is more urgently relevant, whether we think of ourselves in particular or the Church in general, than that we should be aware of heresy. Take the New Testament, take the history of the Christian Church, or take individual Christian experience, and you will see that true doctrine is always urgently relevant. It is of supreme importance for the whole life of the Church. The Holy Spirit is the power in the Church, and the Holy Spirit will never honour anything except His own Word. It is the Holy Spirit who has given this Word. He is its Author. It is not of men! Nor is the Bible the product of 'flesh and blood'.

The Apostle Paul was not simply giving expression to contemporary teaching or his own thoughts. He says, 'I received it by revelation'. It was given to him, given to him by the Lord, the risen Lord, through the Holy Spirit. So I am arguing that the Holy Spirit will honour nothing but His own Word. Therefore if we do not believe and accept His Word, or if in any way we deviate from it, we have no right to expect the blessing of the Holy Spirit. The Holy Spirit will honour truth, and will honour nothing else. Whatever else we may do, if we do not honour this truth He will not honour us.

I would love to continue quoting from this vital chapter, but I have already gone too long here. If you do not have his eight volumes on Ephesians, they are of course well-worth getting. But in the meantime, if you want to read his entire chapter, you will find it here: www.the-highway.com/heresies_Lloyd-Jones.html