A clarification of terms helps somewhat. What Ellul refers to as "morality" coincides to a great degree with what I would call "legalism" - a system of concrete rules that allows for very few exceptions and tolerates no dissent. Although I would argue for disentangling our concept of morality from its legalistic implications without discarding the term entirely, Ellul goes even further than that.
Few Christians would dispute that something can only be good if God calls it good, but to assert that while simultaneously discarding our traditional conceptions of morality is to paint a picture of an arbitrary and potentially unreliable God. In our finite minds, a just God must not only have absolute, unchanging standards but he must fully explain them to us.
To argue so, however, is to expose the limits of our own perspective. "God works in mysterious ways," we agree, even as we demand a framework that we can use to predict everything that God will ever do. Without a list of absolutes that our minds can fully grasp (and thereby use to maintain control over our own lives), our fleshly nature insists that all will dissolve into chaos.
But just because God sometimes appears inconsistent to us does not mean that he truly is inconsistent. God's perspective necessarily encompasses knowledge that we couldn't possibly be aware of, including things which are completely beyond our comprehension. If he were to therefore limit himself to acting in ways that we could fully understand (i.e. according to a known set of "moral absolutes"), he would no longer be free to accomplish any greater good.
If we truly desire a relationship with the Creator of the universe, we must accept that our demands for security and certainty serve only to undermine our ability to have such a relationship. We must be willing to live a life guided by the Holy Spirit, and only by the Holy Spirit.
As Genesis shows us, the origin of sin in the world is not knowledge, as is often said (as though God were interdicting our intellectual development, which would be absurd); it is the knowledge of good and evil. In this context knowledge means decision. What is not acceptable to God is that we should decide on our own what is good and what is evil. Biblically, the good is in fact the will of God. That is all. What God decides, whatever it may be, is the good.
If, then, we decide what the good is, we substitute our own will for God's. We construct a morality when we say (and do) what is good, and it is then that we are radically sinners. To elaborate a moral system is to show oneself to be a sinner before God, not because the conduct is bad, but because, even if it is good, another good is substituted for the will of God.
This is why Jesus attacks the Pharisees so severely even though they are the most moral of people, live the best lives, and are perfectly obedient and virtuous. They have progressively substituted their own morality for the living and actual Word of God that can never be fixed in commandments.
In the Gospels Jesus constantly breaks religious precepts and moral rules. He gives as his own commandment "Follow me," not a list of things to do or not to do. He shows us fully what it means to be a free person with no morality, but simply obeying the ever-new Word of God as it flashes forth.
Similarly, Paul attacks what might seem to be morality in Judaism, rules and precepts laid down by men and not coming from God at all. The great mutation is that we have been freed in Jesus Christ. The primary characteristic of free people is that they are not bound to moral commandments.
"All things are lawful," Paul twice proclaims. "Nothing is impure," he teaches. We find the same message in Acts. We are as free as the Holy Spirit, who comes and goes as he wills. This freedom does not mean doing anything at all. It is the freedom of love. Love, which cannot be regulated, categorized, or analyzed into principles or commandments, takes the place of law. The relationship with others is not one of duty but of love.
When I say that the revelation of God in Jesus Christ is against morality, I am not trying to say that it replaces one form of morality with another. (How many times, alas, we read that Christian morality is superior to all others. This is not even true. We find honest and virtuous people, good husbands, fathers, and children, scrupulous and truthful people outside Christianity, and more perhaps than there are Christians.)
Revelation is an attack on all morality, as is wonderfully shown by the parables of the kingdom of heaven, that of the prodigal son, that of the talents, that of the eleventh-hour laborers, that of the unfaithful steward, and many others. In all the parables the person who serves as an example has not lived a moral life. The one who is rejected is the one who has lived a moral life. Naturally, this does not mean that we are counseled to become robbers, murderers, adulterers, etc. On the contrary, the behavior to which we are summoned surpasses morality, all morality, which is shown to be an obstacle to encounter with God.
Love obeys no morality and gives birth to no morality. None of the great categories of revealed truth is relative to morality or can give birth to it; freedom, truth, light, Word, and holiness do not belong at all to the order of morality. What they evoke is a mode of being, a model of life that is very free, that involves constant risks, that is constantly renewed. The Christian life is contrary to morality because it is not repetitive. No fixed duty has to be done no matter what course life may take. Morality always interdicts this mode of being. It is an obstacle to it and implicitly condemns it, just as Jesus is inevitably condemned by moral people.
To live outside of any man-made system of morality ("biblical" or otherwise) is to open oneself up to risk and uncertainty. It invites contempt from others, even (perhaps especially) from other Christians. Yet true relationship cannot develop until we abandon our "right" to the security of absolute certainty and take that first step into the unknown.