Deuteronomy 8

Moses explained the reason why we experience tribulation as he recounts -

"...thou shalt remember all the way which the LORD thy God led thee these forty years in the wilderness, to humble thee, and to prove thee, to know what was in thine heart, whether thou wouldest keep his commandments, or no.
3 And he humbled thee, and suffered thee to hunger, and fed thee with manna, which thou knewest not, neither did thy fathers know; that he might make thee know that man doth not live by bread only, but by every word that proceedeth out of the mouth of the LORD doth man live."  (Old Testament | Deuteronomy 8:2 - 3)

In my mind, the true test of tribulation is to know what is in our hearts.  Moses adds the analogy -

"Thou shalt also consider in thine heart, that, as a man chasteneth his son, so the LORD thy God chasteneth thee.
6 Therefore thou shalt keep the commandments of the LORD thy God, to walk in his ways, and to fear him."  (Old Testament | Deuteronomy 8:5 - 6)

 Moses even mentions another miracle -

"Thy raiment waxed not old upon thee, neither did thy foot swell, these forty years."  (Old Testament | Deuteronomy 8:4)

As Moses continues his discourse, he explains that all blessings are predicated on obedience.  Most of Chapter 11 touches on this.  A couple of verses include -

"Therefore shall ye keep all the commandments which I command you this day, that ye may be strong, and go in and possess the land, whither ye go to possess it;
9 And that ye may prolong your days in the land, which the LORD sware unto your fathers to give unto them and to their seed, a land that floweth with milk and honey."  (Old Testament | Deuteronomy 11:8 - 9)

"And it shall come to pass, if ye shall hearken diligently unto my commandments which I command you this day, to love the LORD your God, and to serve him with all your heart and with all your soul,
14 That I will give you the rain of your land in his due season, the first rain and the latter rain, that thou mayest gather in thy corn, and thy wine, and thine oil.
15 And I will send grass in thy fields for thy cattle, that thou mayest eat and be full.
16 Take heed to yourselves, that your heart be not deceived, and ye turn aside, and serve other gods, and worship them;
17 And then the LORD's wrath be kindled against you, and he shut up the heaven, that there be no rain, and that the land yield not her fruit; and lest ye perish quickly from off the good land which the LORD giveth you."  (Old Testament | Deuteronomy 11:13 - 17)

Thus -

"I, the Lord, am bound when ye do what I say; but when ye do not what I say, ye have no promise."  (Doctrine and Covenants | Section 82:10)