John Gill's Exposition of the Bible

When I encounter a Biblical passage that is difficult to comprehend, I like to turn to the work of 18th century English theologian John Gill. His Exposition of the Bible, freely available online here, gives a detailed interpretation of every verse in the Bible.

As an example, consider 1 John 5:16-17 (ESV), 

If anyone sees his brother committing a sin not leading to death, he shall ask, and God will give him life—to those who commit sins that do not lead to death. There is sin that leads to death; I do not say that one should pray for that.

Why does this mean? Doesn't God forgive all sin? Paraphrasing John Gill's explanation, "death" doesn't mean death of the body, but rather death of the soul. And the soul dies when we harden our hearts to God and persist in our sinning. Jesus says something similar in Mark 3: 28-29 (ESV),

Truly, I say to you, all sins will be forgiven the children of man, and whatever blasphemies they utter, but whoever blasphemes against the Holy Spirit never has forgiveness, but is guilty of an eternal sin...

So the theme is similar to Daniel's prayer: When we pray, we must submit to God with a humble heart, a heart that acknowledges our shortcomings. And we should do this without ceasing!