In Matthew chapter 6, the Lord Jesus Christ cautions His disciples against praying as the hypocrites (v.5) and the heathen (v.7). He then prescribes a model prayer for His disciples’ use. Prior to the model prayer (or, “Lord’s Prayer” as it is commonly called), Jesus makes this statement in v.8, “For your Father knows the things you have need of before you ask Him.” This statement is a corrective to the technique employed by the heathen: use many words so that God (or the gods) will hear you and answer. Jesus is saying that you cannot manipulate God or control God or exercise certain formulas in order to make God perform; rather, He knows what you need before you ask Him. It is important to notice what Jesus does not say; He does not say, “Your Father knows the things you have need of so don’t bother asking Him.” No, the Lord Jesus says “He knows the things you have need of before you ask Him” – the Lord assumes we will present our petitions before God. This is consistent with the Prophet Isaiah in chapter 65:24, “It shall come to pass that before they call, I will answer; and while they are still speaking, I will hear.” God is a sovereign God and therefore knows the end from the beginning and has certainly decreed all things that come to pass. If God were not sovereign; if God did not decree all things; if God did not possess absolute authority over all things, prayer would be useless.
In light of this biblical truth, people often ask, “Why pray if God is sovereign?” The Scripture gives several reasons why believers ought to pray to a sovereign God. Here are just a few of those reasons. In the first place, prayer is a natural response from the born again child of God. In the discussion concerning prayer in Matthew 6, Jesus does not command believers to pray, He assumes that they will pray. When the Lord speaks to Ananias and tells him to make contact with the newly converted Saul of Tarsus, He describes Saul this way, “Arise and go to the street called Straight, and inquire at the house of Judas for one called Saul of Tarsus, for behold, he is praying” (Acts 9:11). It is true that hypocrites pray (remember Mt 6:5) and therefore we can say that “not all that glitters is gold.” However, it is equally true that gold does in fact glitter and therefore a man who has been brought out of darkness into marvelous light by the sovereign grace of God cannot help but pray. Secondly, prayer is commanded. While Jesus assumes believers pray in Mt 6, the rest of the Bible contains various commands to pray. We might be tempted to think, “if it is part of my life as a new man to pray, why would I have to be commanded to pray?” There are a whole host of things Christians ought to do, but nevertheless they also need to be commanded to do them; such is the way with remaining sin. Thirdly, prayer is an act of worship. God has ordained prayer as a means by which the believer submits to his Father and expresses praise and adoration for His goodness. This facet of prayer is displayed in the life of Job. After having experienced the loss of most everything that was near and dear to him, Job did not seek solace in worldly comforts or books with catchy titles like “Ten Principles on Dealing with Grief.” No, the Scripture says, “Then Job arose, tore His robe, and shaved his head; and he fell to the ground and worshiped. And he said, ‘naked I came from my mother’s womb, and naked shall I return there. The LORD gave, and the LORD has taken away; blessed be the name of the LORD. In all this Job did not sin nor charge God with wrong” (Job 1:20-22). Our difficulties do not lessen the beauty and glory of God. Our difficulties do not remove the obligation or privilege of worshiping God. Upon later reflection, many seasoned saints have witnessed how difficulties drove them to a more earnest worship of their heavenly Father. Fourthly, prayer to a sovereign God is an exercise of the believer’s faith. From time to time books appear or sermons are preached which maintain the unbiblical notion, “prayer changes God.” Prayer does not change God, but rather prayer changes us. God is our Rock, He is unchanging, and He is all powerful. It is not God that needs to change; we need to change. In prayer, the believer’s faith is exercised, his dependence upon God is strengthened, and slowly but surely, the believer is conformed to God’s will. Finally, prayer is a means by which the believer may unburden himself with One who cares for him, as Peter writes, “casting all your care upon Him, for He cares for you” (1 Pet 5:7). Calvin summarizes in this manner,
“Believers do not pray, with the view of informing God about things unknown to Him, or of exciting Him to do His duty, or urging Him as though He were reluctant. On the contrary, they pray, in order that they may arouse themselves to seek Him, that they may exercise their faith in meditating on His promises, that they may relieve themselves from their anxieties by pouring them into His bosom; in a word, that they may declare that from Him alone they hope and expect, both for themselves and for others, all good things.”
In conclusion, the believer must also realize that prayer does not exist in isolation from the Bible. The Bible informs us concerning God, His being, His attributes, and His purpose in the world and with His people. We must know Him as God through our Lord Jesus, trust Him as our heavenly Father, and realize that He has purposed to work all things for good for His people (Rom 8:28) which even includes difficulties, trials, and tribulations. With this understanding of prayer, perhaps the more legitimate question is, “Why pray if God is not sovereign?”
 John Calvin, A Harmony of Matthew, Mark, Luke (trans. William Pringle; Edinburgh: T&T Clark, 1840; repr., Grand Rapids: Baker, 1996), XVI, p.314.