Why do missionary work?

In the year 1791 the Moravians detailed their motivation for missionary work. That statement is below the line. To enhance my focus in an otherwise tedious statement I have highlighted words that I believe are key.  

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“The simple motive of the brethren for sending missionaries to distant nations was and is an ardent desire to promote the salvation of their fellow men, by making known to them the gospel of our Savior Jesus Christ. 

It grieved them to hear of so many thousands and millions of the human race sitting in darkness and groaning beneath the yoke of sin and the tyranny of Satan; and remembering the glorious promises given in the Word of God, that the heathen also should be the reward of the sufferings and death of Jesus; and considering His commandment to His followers, to go into all the world and preach the gospel to every creature, they were filled with confident hopes that if they went forth in obedience unto, and believing in His word, their labor would not be in vain in the Lord. 

They were not dismayed in reflecting on the smallness of their means and abilities, and that they hardly knew their way to the heathen whose salvation they so ardently longed for, nor by the prospect of enduring hardships of every kind and even perhaps the loss of their lives in the attempt. Yet their love to their Savior and their fellow sinners for whom He shed His blood, far outweighed all these considerations. They went forth in the strength of their God and He has wrought wonders in their behalf.”