“For which of you, desiring to build a tower (farm mansion), does not first sit down and count the cost, whether he have that with which to complete it? Lest haply, when he has laid a foundation, and is not able to finish, all that behold begin to mock him,”
But Jesus does not want them to take the decision lightly, and therefore illustrates this in terms of a builder of a tower or ‘large farm house' (a farmhouse on the grand scale - many of his hearers would be farmers). Does not such a builder work out the cost before laying the foundation? For there is little point in laying the foundation if he will not be able to finish building the house. This brings out the size of the enterprise. It is no light thing that he is taking on.
But if he lays the magnificent foundation and then is unable to do any more work because the money has run out everyone will jeer at him and mock him. Why had he been such a fool? Why had he tried to participate in such a grand scheme? So in order to avoid this he should prepare a budget beforehand in order to ensure that he has enough to finish the project. And then he may make his free choice as to whether to go ahead or not (compare the men in Luke 9:57-62).