Calvin summaries the situation very well.
In fact, the distinction between latria and dulia, as they called them, was invented in order that divine honors might seem to be transferred with impunity to angels and the dead.
For it is obvious that the honor the papists give to the saints really does not differ from the honoring of God. Indeed, they worship both God and the saints indiscriminately, except that, when they are pressed, they wriggle out with the excuse that they keep unimpaired for God what is due him because they leave latria to him.
But since the thing itself, not the word, is in question, who can permit them to make light of this most important of all matters? But — to pass over this also — their distinction in the end boils down to this: they render honor [cultus] to God alone, but undergo servitude [servitium] for the others.
For latreia, among the Greeks means the same thing as cultus among the Latins; douleia properly signifies servitus; and yet in Scripture this distinction is sometimes blurred. But suppose we concede it to be unvarying. Then we must inquire what both words mean: douleia is servitude; latreia, honor. Now no one doubts that it is greater to be enslaved than to honor. For it would very often be hard for you to be enslaved to one whom you were not unwilling to honor.
Thus it would be unequal dealing to assign to the saints what is greater and leave to God what is lesser. Yet many of the old writers used this distinction. What, then, if all perceive that it is not only inept but entirely worthless? -Calvin's Institutes, 1:12:2