How important should the LXX be for Christian preaching?

Lamentations 4:20 was an important christological reference to many of the church fathers (such as Justin Martyr, Tertullian, Cyril of Alexandria, and Augustine) and is a good example of how the LXX guided early Christian interpretation.

Possible Hebrew Translation:*
[The] breath of our nostrils, YHWH’s anointed,
was captured in their pits –
[He of] whom we said, “In his shade,
we will live among the nations.”

Majority Christian Rendering of the LXX:*
The s/Spirit before our face, Christ the Lord,
was taken in our/their corruptions/snares,
of whom we said, “In his shadow,
we shall live among the Gentiles.”

“A christological re-reading of the passage opens up interesting new ways of construing it. The capture of the king in 4:20 is the climax of the woes in the chapter: he who embodied the whole nation representatively has fallen to the foe. Immediately after this we have the unexpected oracle of salvation (4:21-22), with no hint in the text as to how one could move from the lowest point to the highest point of hope in the book….
On a christological interpretation, the move from verse 20 to verse 21 makes perfect sense. The loss of the king of Israel to the pagan foe in 4:20 is simultaneously the climax of the exilic woes and the means by which those woes come to an end…. The violence of the enemy is engraved on the subjugated and broken body of the Messiah, and yet in the act of being overcome by evil the evil is itself overcome by nonviolence. A subversive, cruciform element is introduced in the reception of the text.”*

* from Lamentations, Robin A. Parry (188-190)