"For the word of God is living and active and sharper than any two-edged sword, and piercing as far as the division of soul and spirit, of both joints and marrow, and able to judge the thoughts and intentions of the heart," (Hebrews 4:12).
* "piercing" This aspect of the Word's penetrating power is graphically recounted in Acts, chapter 2, verse 37. Peter has just concluded his Spirit-anointed sermon, demonstrating with crystal clarity that the Old Testament-predicted Messiah is the same Jesus who was crucified by his hearers! Luke then tells us that "...when they heard this, they were pierced to the heart..."
John MacArthur comments, "the Greek word for 'pierced' means 'stab,' and thus denotes something sudden and unexpected." When the Spirit of Truth sees fit to apply His Word of Truth to the human heart, it is stunning. In this situation Peter's hearers cried out for instruction ("...what shall we do?"). And, they were not interested in information, so much as relief! They had to respond. The Word's piercing requires a response!