Misplaced shame is a mountain in the way of missions. Jesus means for us to cast it into the sea. “If you have faith…it will be done” (Matthew 21:21ff).
The jagged mountain of shame becomes a highway for missionary joy when we blast it away with the bombshells of Bible promises. How many megatons of power are in these shame-blasting promises?
Fear not, for you will not be ashamed; be not confounded, for you will not be put to shame; for you will forget the shame of your youth, and the reproach of your widowhood you will remember no more. For your Maker is your Husband, the Lord of hosts is his name (Isaiah 54:4-5).
The Lord God helps me; therefore, I have not been confounded; therefore, I have set my face like a flint, and I know that I shall not be put to shame. He who vindicates me is near. Who will contend with me? Let us stand up together! (Isaiah 50: 7-8).
I am not ashamed of the gospel, for it is the power of God unto salvation(Romans 1:16).
I suffer (as a missionary) but I am not ashamed, for I know whom I have believed, and am persuaded that he is able to guard until that day what has been entrusted to me (2 Timothy 1:12).
If you are reproached for the name of Christ, you are blessed, because the spirit of glory and of God rests upon you… If one suffers as a Christian, let him not be ashamed, but under that name let him glorify God (1 Peter 4:14, 16).
God means to blast the mountain of shame out of the way and make it a highway for missionary zeal. “Every mountain and hill shall be brought low…and all flesh shall see the salvation of our God” (Luke 3:5).
Shame tries to cancel your missions commitment in two ways. You can feel that you’re not good enough for missions. Or we can feel that missions is not good enough for you. Shame for sin can keep you away, and shame for God can scare you away. You can feel crushed beneath the shame of sin, or you can feel comfortable above the shame of the cross. In either case shame wins and you lose.
But this is not the will of Christ for you. “Your sins are forgiven. Your faith has saved you. Go (forth to mission!) in peace” (Luke 7:48, 50). And do not fear the world’s shame. God’s honor makes all the difference. “If anyone serves me, the Father will honor him” (John 12:26). So let us go on from strength to strength in the courage of God's promises: "He who believes in him will not be put to shame" (1 Peter 2:6); "No one who beleives in him will be put to shame" (Romans 10:11); therefore, "Do not be ashamed then of testifying to our Lord" (2 Timothy 1:8).
John Piper, A Godward Life, p. 179-180