Now these are David's last words...
...Neither is my house so great with God, that he should make with me an eternal covenant, firm in all things and assured.
For he is all my salvation, and all my will; neither is there aught thereof that springeth not up.
But transgressors shall all of them be plucked up as thorns which are not taken away with hands.
And if a man will touch them, he must be armed with iron and with the staff of a lance; but they shall be set on fire and burnt to nothing.
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In this small excerpt from King David's last words as he lay dying he is affirming that there are no guarantees by God for grace to his house and family. David knows that the covenant with Israel does not exist for biological family reasons or for merit of David and his family but because of God's grace alone. So King David takes this opportunity to warn his people that while there is a covenant, it is not a guarantee that is based on biological, rank, relationship or other human merit but completely due to the grace of God to the faithful. This is the second part of what King David warns that the covenant does not protect those who are unfaithful. Transgressors even "within" the covenant by virtue of their having transgressed will be plucked out of the salvation and graces of the covenant and burned until there is nothing left of them (not even ash).