The entire goal of Christian missions is to take the truth of the Gospel, in all it breadth and depth, to the world. The Gospel of Jesus Christ is an exclusive message, one that cuts across the grain of all of the cultures that have arisen among men for millennia. Because biblical truth meets man where he is, but seeks to transform him into the likeness of Christ, all true Christian missionary endeavor is a manifestation of genuine cross cultural ministry. There are at least five clear reasons that such endeavor demands formal Bible study.
The Bible is the only Trustworthy Revelation of God's Redemptive Work in Reaching Fallen Man
Because this is true, and because there are so many other religious paradigms the Christian missionary will encounter, it is imperative that he have more than a passing knowledge of all that the Bible teaches. Failure to have such biblical knowledge could be a fatal flaw in his efforts to reach the lost.
The Redemptive Truth of the Bible can only be fully grasped in its Full Context
A partial grasp of [or adherence to] biblical truth results in pseudo-Christian cults. The only safeguard against mixing God's truth with religious error lies in a full grasp of and adherence to the truth of the Bible in its entirety. Even in the best of circumstances the Enemy is always hard at work to mix in foundational error with the truth.
God's Truth must be taken as He Has Given It
This demands that the servant of the Lord become familiar with all of Scripture. God's revelation of truth in the Bible is given perfectly. No man may improve upon it. Thus, every genuine servant of the Lord needs to become biblically literate far beyond what has become the norm in American churches. And, this demands even more of those who are taking the truth to places where the indigenous peoples have no familiarity with Scripture at all.
The Entire Bible is Evangelistic
Contrary to ordinary expectations, everything in the Bible is quite evangelistic. The missionary does well to refuse to limit himself to a grasp of passages that have historically been labeled as being evangelistic [for example the 'Romans Road']. Psalm 23 is wonderfully evangelistic in that it invites those for whom the Lord is NOT their shepherd to come to the Shepherd of the stars for an entirely new life. Ephesians presents unreachable riches in Christ that can only be accessed through coming into a right relationship with God through Christ. There are literally examples without number all throughout the Scriptures of both the Old and the New Testaments.
All of Scripture is Profitable for God's Purposes
2 Timothy 3:15-17 makes it absolutely clear that all of Scripture is profitable for equipping the man of God for the fulfillment of His redemptive purposes in life. We are told that it is profitable for doctrine, for reproof, for correction and for instruction in righteousness. Since this is true for 'all Scripture,' the missionary does well to become a serious student of all of Scripture.
The missionary who gives himself to become a student of all of Scripture places himself before God for the fulfillment of His wise redemptive purposes through his life. It is the only way such a servant may be sure that he is presenting a fully biblical Gospel message.