If prayer is merely 'talking to God', what are we hoping to communicate to Him that he doesn't already know? If God has a pre-ordained plan, what are we hoping to achieve when we ask him to divert from his deterministic designs? Are we hoping to change the mind of, or communicate something unknown to, a sovereign, almighty God?
In the first instance, we should not overlook the fact that prayer is commanded in scripture. 1 Thessalonians 5:17, amongst other verses, make clear that God commands us to pray to Him. So, on one level, we should bother with prayer because God commands us to pray. However, whilst this asserts why we ought to pray it doesn't explain why God wants us to pray in the first place. The real question revolves around why a sovereign God commands us to pray when he already knows our thoughts and is in control of everything.
We can glean from Daniel 4:35, Proverbs 19:21, Ephesians 1:11, et al that God is sovereign and in control of everything. Rather than causing us to ask why we should bother with prayer these verses should give us real encouragement to engage in prayer. For, if God is not sovereign, what point is there in asking him to do anything when it is likely beyond his power? It is specifically because God has the power to change events and human hearts that prayer is of any value at all.
Nevertheless, although the sovereignty of God should cause us to see value in prayer, we are still led back to the original question. If God is in control and works everything ‘according to the counsel of his good will’,
why bother bringing anything to Him when he will do as he wills anyway? What exactly are we hoping to achieve through prayer?
In 2 Corinthians 1:10-11, Paul speaks about prayer in a rather unexpected way. He appears to suggest that God's divine will is specifically fulfilled as a result of 'the prayers of many'. Thomas Aquinas picks up this theme in Summa Theologiæ and argues "we do not pray in order to change the decree of divine providence, rather we pray in order to acquire by petitionary prayer what God has determined would be obtained by our prayers". In short, when we pray it is because God, in his sovereignty, has moved us to pray. When our prayers
are granted it is because God willed us to pray and, through our prayers, he
willed to work.
Although God can, and will, bring about his purposes by his own strength, he has stated the way in which he wants those purposes to to be worked out. God wants to work out his purposes through the prayers of his people. Indeed, this is part of God's rich grace toward us. He can save whomever
he wants, heal whomever he wants and bring about whatever events he wants
without interference yet God, in his grace, actively includes us in his plan
by making prayer the means by which he brings about his divine purposes. When we pray, we are actively - rather than passively or deterministically - participating in God's divine plan. God wills us to pray and, through our prayers, he is pleased to work.
Our prayers are the means by which God works out his plans and purposes. We are active participants in God's plan when we pray. By his grace, we are included and associated in the working out of his sovereign and perfect plan - we play an active part in all that God decrees is good - when we pray.
This same truth is why we should engage in evangelism and mission. Yes, the Lord commanded us to do it; and yes, God is sovereign and can save whomever he wills without our help. However, God has determined the way he wants to draw people to himself and enlarge his kingdom. He calls us to evangelise and engage in mission because he wants to graciously include us in his plan of salvation. We are associated with the ultimate good of bringing people to a knowledge of Christ, to a position where they can glorify God and enjoy him forever, when we engage in evangelism and the Lord chooses to work through us.
When a child helps their parent bake a cake, the work may take longer and there may be more mess in the kitchen, but there can be no doubt the child most definitely helped. Though it would be easier to do it themselves, in allowing the child to help, a parent gives a sense of ownership of the task to the child and allows them to learn something otherwise unattainable. Similarly, although the Lord could do it faster and with less mess without our help, just like the child in the kitchen, he graciously allows us to be part of his perfect plan. We can lay claim to active involvement in God's plan because we, albeit in our small and clumsy way, most definitely helped. We are given an opportunity to grow in ways that would be utterly unattainable were God to enact his plan without reference to us.
Prayer and evangelism are God's most gracious ways of actively including us in his plan and are a significant source of growth in the Christian life. Our question should not be 'why should I bother?' but rather 'why would I not?'.