King David and John the Baptist were both men of God, yet one died peacefully after reigning for forty years and the other died a premature, violent death. Sirach, in praising David's life, stressed only the parts where he did the will of God. Where David had strayed, Sirach is silent except to say in verse 11 'The Lord took away his sins." This is rightly so, for David, even when sinning, was always conscious of the offence he gave God, and he made it a point to repent and make amends to the extent that his love for God shone through.
John the Baptist also loved and served God in a shining way. A man of great principles, he was austere and self-sacrificing. He demanded of his followers that they too give up everything to follow God. He knew the need of sinners to repent of their follies and preached this even to the high and mighty of the land. This ultimately led to his death, as this passage by Mark reveals.
Mark's account of John's death is meant to show him as a precursor of Jesus even unto death. John's fate was a portent of Jesus' fate. Hence Mark chooses to narrate it at this point of his gospel when the disciples had just been sent out to preach the coming of the Kingdom of God. This suggests that their mission, coinciding with the death of John, was preparatory to a full Christian mission after Jesus' death.
Lord, help us to live our lives in accordance with Your will even in death!