This quote from Wm. Paul Young's The Shack is often interpreted as promoting universalism, but I find it can be used as an illustration of God's irresistible grace:
If you are among God's elect, then He will travel any road, among any nation and tribe, to call you unto Himself. Rather than forcing you, kicking and screaming, into heaven, God's irresistible grace transforms your will and desires, so that you joyfully march on as a child of the Lord.
Revelation 5:9
And they sang a new song, saying,
“Worthy are you to take the scroll
and to open its seals,
for you were slain, and by your blood you ransomed people for God
from every tribe and language and people and nation.”
This is from the 1689 London Baptist Confession, which was adapted from the Westminster Confession:
God can save whoever He pleases, even those who never hear the Gospel, "who are incapable of being outwardly called by the ministry of the Word."
The Shack's story of an Indian princess who gives up her life to save her people can also be interpreted as supporting the doctrine of limited atonement.
Matthew 1:21, Luke 1:68, John 10:11, John 15:13
When reading a work of fiction, it can be interpreted in various ways, regardless of the author's own beliefs. This section of the Shack wonderfully illustrates the Reformed doctrine of salvation by faith alone through grace alone:
According to Martin Luther and John Calvin, the true purpose of the law is to serve as a mirror of our own sinfulness, so that we will be convicted of our need for a savior. Anything we do out of obedience to the law is in gratitude for, rather than a condition of, our salvation.
This line from the film adaptation of The Shack answers the question of what’s the purpose of prayer if God foreknows everything that comes to pass anyway:
A lot of the backlash that The Shack received may have been due to sexism and racism. If God can appear as a dove, an angel, a burning bush, pillars of cloud and fire, a baby in a manger, etc., then He can appear as a black woman if He so chooses. Psalm 115:3, Psalm 135:6