All 4 Uses

therefore
in
The Aeneid
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Heed therefore what I say; and keep in mind What Jove decrees, what Phoebus has design'd, And I, the Furies' queen, from both relate You seek th' Italian shores, foredoom'd by fate: Th' Italian shores are granted you to find, And a safe passage to the port assign'd.†
Book 3

therefore = for that reason
'Besides, if faith to Helenus be due, And if prophetic Phoebus tell me true, Do not this precept of your friend forget, Which therefore more than once I must repeat: Above the rest, great Juno's name adore; Pay vows to Juno; Juno's aid implore.†
Book 3
Unknowing of a train conceal'd so well, She fear'd no worse than when Sichaeus fell; Therefore obeys.†
Book 4 *
He scarcely knew him, striving to disown His blotted form, and blushing to be known; And therefore first began: "O Tsucer's race, Who durst thy faultless figure thus deface?†
Book 6

Definitions:

(1) (therefore)
for that reason (what follows is so because of what was just said)
(2) (meaning too rare to warrant focus)