I'm going to quote some recent statements by Paul Helm:
Following on from this, while how the ‘two wills’ of God are elements of one divine will is ‘inscrutable’ to us, I suggest that nevertheless there is a fittingness, even perhaps a necessity to the indiscriminate offer of grace in a situation in which salvation is freely given and the enjoyment of that grace is through justification by faith alone and its inseparable accompaniment, sanctification. Perhaps we may put the point as strongly as this: The execution of the one divine will of salvation through free grace must have different phases if the freeness of grace is to be received as such, and preserved from serious misunderstanding or even compromise. As we have seen, on Calvin’s view there are not two wills in God, but different elements of the one will. The one will not only has differential outcomes, in the case of the elect and the reprobate, but it is also brought to pass through various phases. These are not (in this case) the much-discussed covenantal or redemptive-historical phases, but phases in which those elected and reprobated are in different epistemic situations, phases in which certain outcomes must be hidden from those about to enjoy them, if they are to receive them with understanding.
The Lord’s one will is decretal, distinguishing between election and reprobation, but there is a phase in the execution of that decree, let’s call it the ‘proclamation phase’, in which the presentation is worded universally. From that universal presentation no inferences can be drawn as to who among those to whom the presentation is made are reprobate, and those who are elect. Discriminate grace, but indiscriminate preaching.
Why is there this phase? Why is it that ‘announcement’ is a part of the scheme? Why does God choose to bring his grace to sinners by means of an announcement that anyone who turns from his sin will be received? Partly, of course, because it is true! Whoever wills may come. God does desire the return of the penitent sinner. But suppose for a moment that there was no such phase, but instead an economy which was conducted uniformly, either in terms explicitly directed to the elect, or in terms directed explicitly to the reprobate. If this happened (as it tends in fact to happen in some hyperCalvinist settings) the hearers would not be invited to come to Christ, but (by the terms of the preaching) they would be forced to ask ‘Which am I? Am I among the elect, or among the reprobate? Do I fulfil the requirements or conditions of being among the former or among the latter?’ In these circumstances there could be no full, direct invitation. The gospel could not be proclaimed ‘by invitation only’. In other words, under such terms ‘gospel preaching’ would have the effect not of turning men and women to face a Christ who invites them to come to him, but of turning them in upon themselves. And such a turning in is but a very short step from a person being concerned about whether or not he is qualified to come to Christ. Or concerned about the hardness of his heart, in which case there would be despair over what would be taken to be the marks of retribution. Either way, instead of facing Christ a person would introspect. At such a point grace would become legalised. So I suggest that what Calvin is identifying is not an arbitrary procedure on God’s part, but a necessary feature of the preaching of God’s free grace in Christ. This is a pastoral necessity, and perhaps even a logical necessity. So while God’s procedure is ‘ineffable’ in the sense that it is difficult to see how the one will of God possesses different phases, there is a rationale for it.
It would also have implications for prayer and more generally, for the desire for the salvation of men and women. For example, if, after setting forth in Romans Ch. 9 his theology of the remnant according to grace, Paul had known by some means who among his Jewish contemporaries were elect, and who reprobate, how could he have had a desire that they might (without exception) be saved (Rom.10.1), or had the thought that he might be accursed form Christ for the sake of his brothers, his kinsmen according to the flesh? (Rom. 9.1-5).