Because Apostle Paul understood that spiritual insight into God’s word/truth can only come from the Holy Spirit revealing it to us, he confidently and faithfully asked God to do so when in prayer for those he ministered to, because he knew the Holy Spirit was the one doing the work in their hearts.
Now it’s impossible for someone to grow effectively without receiving the anointed word of God (Hebrews 11:6, Romans 10:17, Joshua 1:7-8, Psalm 119, James 1:23, 1 Peter 1:23, Romans 12:2) ... But if the word was all that’s required for spiritual growth, then why would he be led to pray for it as well?
It tells us that Paul didn’t rely solely on the word/letters he wrote to the churches to ensure that they grew spiritually, he also prayed for them to grow. Based on this revelation, Paul - inspired by the Holy Spirit to write these words (meaning it's something God is saying we can do) - prays for spiritual growth in the lives of those entrusted to his care/the churches/believers everywhere. Meaning we can pray these prayers as well and fully expect God to watch over His word to perform it!
Let's take a look at a few examples of this in the Bible:
Phil 1:9-11 (NLT)
I pray that your love will overflow more and more, and that you will keep on growing in knowledge and understanding. For I want you to understand what really matters, so that you may live pure and blameless lives until the day of Christ’s return. May you always be filled with the fruit of your salvation—the righteous character produced in your life by Jesus Christ—for this will bring much glory and praise to God.
2 Thessalonians 1:11-12 (NIV)
With this in mind, we constantly pray for you, that our God may count you worthy of his calling, and that by his power he may fulfill every good purpose of yours and every act prompted by your faith. We pray this so that the name of our Lord Jesus may be glorified in you, and you in him, according to the grace of our God and the Lord Jesus Christ.
Colossians 1:9-11 (AMP)
For this reason we also, from the day we heard of it, have not ceased to pray and make [special] request for you, [asking] that you may be filled with the full (deep and clear) knowledge of His will in all spiritual wisdom [in comprehensive insight into the ways and purposes of God] and in understanding and discernment of spiritual things-That you may walk (live and conduct yourselves) in a manner worthy of the Lord, fully pleasing to Him and desiring to please Him in all things, bearing fruit in every good work and steadily growing and increasing in and by the knowledge of God [with fuller, deeper, and clearer insight, acquaintance, and recognition]. [We pray] that you may be invigorated and strengthened with all power according to the might of His glory, [to exercise] every kind of endurance and patience (perseverance and forbearance) with joy
Ephesians 1:17-18 (AMP)
[For I always pray to] the God of our Lord Jesus Christ, the Father of glory, that He may grant you a spirit of wisdom and revelation [of insight into mysteries and secrets] in the [deep and intimate] knowledge of Him, By having the eyes of your heart flooded with light, so that you can know and understand the hope to which He has called you, and how rich is His glorious inheritance in the saints (His set-apart ones)
Ephesians 3:14-19 (NIV)
For this reason I kneel before the Father, from whom every family in heaven and on earth derives its name. I pray that out of his glorious riches he may strengthen you with power through his Spirit in your inner being, so that Christ may dwell in your hearts through faith. And I pray that you, being rooted and established in love, may have power, together with all the Lord’s holy people, to grasp how wide and long and high and deep is the love of Christ, and to know this love that surpasses knowledge—that you may be filled to the measure of all the fullness of God.
Also see below examples of other areas the Bible says we can pray for:
You can pray for your president/prime minister, etc:
1 Timothy 2:1-6 (NKJ)
Therefore I exhort first of all that supplications, prayers, intercessions, and giving of thanks be made for all men, for kings and all who are in authority, that we may lead a quiet and peaceable life in all godliness and reverence. For this is good and acceptable in the sight of God our Savior, who desires all men to be saved and to come to the knowledge of the truth. For there is one God and one Mediator between God and men, the Man Christ Jesus, who gave Himself a ransom for all, to be testified in due time.
You can pray that God will protect someone from falling spiritually ("backsliding"):
Luke 22:31-32 (NKJ)
And the Lord said, “Simon, Simon! Indeed, Satan has asked for you, that he may sift you as wheat. But I have prayed for you, that your faith should not fail; and when you have returned to Me, strengthen your brethren.”
You can pray that God would send out laborers to those who don’t know Him:
Luke 10:2 (NKJ)
Then He said to them, “The harvest truly is great, but the laborers are few; therefore pray the Lord of the harvest to send out laborers into His harvest.
You can pray that God would give you boldness to preach His word:
Ephesians 6:19 (NIV)
Pray also for me, that whenever I open my mouth, words may be given me so that I will fearlessly make known the mystery of the gospel.
You can pray that others fulfill God’s will for their lives:
Colossians 4:12 (NKJ)
Epaphras, who is one of you, a bondservant of Christ, greets you, always laboring fervently for you in prayers, that you may stand perfect and complete in all the will of God.
In the next few messages we'll be looking at examples of men God worked through in the area of evangelism and the role they said prayer played in their ministry.