Some time ago while I was teaching discipleship training, a very important question came up. One of the participants with conviction in her heart, given the content, shared a concern. “How can we pray effectively for missions?” – She asked. – Although “going” or “giving” for missions is regularly emphasized, for some it is not clear how should we pray for missions. Scriptures are clear about Missions. The Great Commission, Paul’s missionary efforts, and the character of God point to missions being the responsibility of every Christian. We must get involved. And of the different types of involvement, nothing is more relevant than prayer. Even if we are going to the field, prayer is not a nice accessory, but an imperative necessity. In my opinion, there is a better way to respond to the question of “how to pray”. If we can understand “why” we must pray for Christian missions, the “how” will come altogether. Here I share some reasons to pray for it, in order to respond how do we should pray.
We Must Pray for Christian Missions…
…because Christ commanded us to pray
Our Lord commands us to pray for His kingdom to come. In other words, Christ commanded us to pray for the extension of his rule in the hearts of those who do not yet know him, and for the consummation of his eternal reign.  Missions are an essential part in such an extension of the kingdom.  In addition, Christ also commanded us to pray for more workers prepared to go to the field as instruments of salvation. 
…because missionary work is God’s work
It is impossible to do God’s work without God! In addressing how his disciples would bear fruit, Jesus said: “…because you can do nothing without me.”  This is why when referring to his missionary work Paul went so far as to say, “Who is adequate for these things?”  We are not powerful or adequate, but God is. And we must pray to see His power and presence with His people in His mission.
…because it is God’s will to answer this prayer
This reason is linked to the previous one. If he has commanded us to pray for outreach work, then in doing so we are doing his will and not our own. There are sweet promises connected with praying according to God’s will. Here are two of them:
This is the confidence we have before him: If we ask anything according to his will, he hears us. And if we know that he hears whatever we ask, we know that we have what we have asked of him. – 1 John 5:14-15
Whatever you ask in my name, I will do it so that the Father may be glorified in the Son. If you ask me anything in my name, I will do it. – John 14:13-14
…because of the Spiritual Battle
Bringing the gospel to our neighbors and to the nations is a spiritual battle. Therefore we must use the armor of God as part of our action in it.  With this in mind, as Paul instructs the Ephesians about this, he not only includes prayer as part of the spiritual armor of every Christian, but specifically asks the brethren to pray for him in his missionary work.  In his book Quiet Talks on Prayer, S.D. Gordon discusses the role of prayer in the spiritual battle and concludes: “Prayer from God’s side is communication between Himself and His allies in the enemy’s country.” Let us pray constantly for missionary work!
…because of the love for the lost
In Romans 10 we find one of the more profound expressions of love in Paul’s ministry. Speaking about his fellow citizen of Israel, he says, “My heart’s desire and prayer to God concerning them is for their salvation.  Desiring the salvation of the lost is an expression of God’s loving character. Such a heart is not only expected of men like Paul, but of everyone who has experienced the gift of salvation. Since God is the only one who can give life to those who are “dead in their trespasses”  we must compassionately pray for them.
…because this glorifies God
This is the strongest reason. The missions are born in the heart of God not in that of men. When we pray for the lost, when we intercede for overseas brothers and sisters, when we pray for foresight to reach places that have not been reached, we are tuning our prayer to the desire of God, who delights to save. Let us pray like the psalmist:
“May God be gracious to us and bless us; may he make his face shine upon us so that your way may be known on earth, your salvation among all nations.” – Psalm 67:1-2
How Can You pray for Christian Missions?
Pray for courage for those who proclaim the gospel.
Pray for the lost who hear / will hear the Word of God
Pray for yourself. May God increase your involvement in his Mission.
Pray for your church. For God to use it as an instrument of missionary outreach.
Pray for provision. For God to meet the spiritual, emotional and physical needs of missionaries and their families.
Pray that God will continue to open doors in places where it is difficult or impossible to proclaim the gospel.
Some Actions to Consider
Consider setting a time to pray for missions.
Consider using some resources and systems. 
Consider involving others (prayer partners). 
Consider being in contact with the missions for whom you pray. So you can also pray (or provide) for specific needs.
Consider praying for missionary work right now.
 Operation World has been a resource that my family and I have used to pray for God’s work in different countries. Books like Quiet Talk on Prayer and Praying with Paul (D. A. Carson) propose some systems.