The following ten reasons why God may delay an answer to prayer come from the book Godly Prayer and Its Answers by John Brown of Wamphray (1609-1679). They all fall under proposition five in his chapter on “God’s Answering of Prayers Cleared” (Chapter 23). These are just the main headings. For each point, Brown goes into further detail and gives Scriptural examples. It’s a good reminder that God’s delays are not necessarily God’s denials.

Proposition 5: We must not think that every delay to give us a return to our prayers is a denial of an answer. God may think it good to delay our answer and yet give it at length … and that for wise and holy ends, as:

1) To teach us all due submission and reverence and to know that He is an absolute God.

2) To teach us patience in waiting at the posts of His door.

3) To try our faith, if we can believe His word and rest on His promise and live in hope.

4) To stir up and awaken us to be more earnest and serious in our petitions.

5) To cause us to prize the mercy more and make it the more welcome when it comes.

6) To put us in case to remark more the faithfulness and goodness of God, when after a long delay He has made good His faithful promise.

7) To fit us more for the mercy that we are asking and to put us in better case to receive it and to improve it.

8) He may delay to give the good things we ask until His own appointed time come, wherein He sees the granting of the mercy will be more for His own glory and give more occasion for setting forth of His praise.

9) He may delay until He have many petitions to answer at once—whether many of our own or the petitions of many others with ours. This is so that thus thanks may be given by many together for one and the same mercy, whether granted to persons (as 2 Cor. 1:11) or to a land.

10) Some mercies sought after may be more fit for the posterity than for the present generation, and therefore they must be delayed.

 
Godly Prayer and Its Answers by John Brown of Wamphray (pp. 275-276)