Prayer is intricately related to missions. The advancement of God's Kingdom into dark places where Satan reigns is a war that Satan will not give up easily. The mission field is one of the primary battlefronts of spiritual warfare. In many places in the Bible missionaries ask for prayer, including Rom. 15.30, Eph. 6.19-20, Phil. 1.19, and Col. 4.3.
Among the few things that Jesus mentions specifically for prayer is the command to pray for missionary workers in Matt. 9:37-38.
Prayer is unique among missionary endeavors because it is not limited in geography, language, culture, or specialized training. Any believer can pray. Pray is one of the key weapons of spiritual warfare. It is a call to heaven-sent, “laser-guided” support, assistance, protection, etc. for people and ministry taking place thousands of miles away.
God promises to hear and answer sincere and faithful prayers according to His will. And, we know that it is His will to glorify Jesus among all nations and through our instrumentality to bring some from every tongue, tribe, and nation to worship Him before the Throne of God in heaven. (see Revelation 5:9; 7:9) So, we have assurance that our prayers so directed will be effective.
Operation World: The Definitive Prayer Guide to Every Nation