The apostle Paul admonished the Ephesian church to pray for him. We can apply that exhortation to our prayers for those God has called to preach the Gospel:

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, for which I am an ambassador in chains. Pray that I may declare it fearlessly, as I should.
Ephesians 6:19-20

Courage is required to speak up in a world full of hostile anti-Christ and anti-biblical misinformation. Even preachers have found themselves muzzled regarding clear biblical teaching. Paul warned Timothy:

But mark this: There will be terrible times in the last days. People will be lovers of themselves, lovers of money, boastful, proud, abusive, disobedient to their parents, ungrateful, unholy, without love, unforgiving, slanderous, without self-control, brutal, not lovers of the good, treacherous, rash, conceited, lovers of pleasure rather than lovers of God—having a form of godliness but denying its power. Have nothing to do with them.
2 Timothy 3:1-5

But Timothy was also encouraged to keep preaching anyway. He was not to give in to those who didn't want their sins and attitudes rebuked.

…I remind you to fan into flame the gift of God, which is in you through the laying on of my hands. For God did not give us a spirit of timidity, but a spirit of power, of love and of self-discipline.
So do not be ashamed to testify about our Lord, or ashamed of me his prisoner. But join with me in suffering for the gospel, by the power of God, who has saved us and called us to a holy life—not because of anything we have done but because of his own purpose and grace….I am not ashamed, because I know whom I have believed, and am convinced that he is able to guard what I have entrusted to him for that day.
2 Timothy 1:6-12

Peter and John of the early church were commanded by religious and civic leaders “not to speak or teach at all in the name of Jesus” (Acts 4:18).

When they reported this to the believers, they joined together in prayer. Their prayers were heard:
After they prayed, the place where they were meeting was shaken. And they were all filled with the Holy Spirit and spoke the word of God boldly.
Acts 4:31

Did you notice that “all” were filled with the Holy Spirit and “all” spoke boldly? The account goes on to report that “with great power the apostles continued to testify to the resurrection of the Lord Jesus, and much grace was upon them all” (Acts 4:33).

Praying to God for his word to be spoken boldly is participating in sending the life giving message of Jesus Christ out to all the world and in this way participate in God's answer to our prayers for his kingdom to come.