A warning against leagues with sinners and sin:
Hezekiah thought himself very happy in the friendship of Babylon, though it was the mother of harlots and idolatries; but Babylon, who now courted Jerusalem, in process of time conquered her and carried her captive. Leagues with sinners, and leagues with sin too, will end thus; it is therefore our wisdom to keep at a distance from them.
~ Matthew Henry on Isaiah 39
Source: http://www.puritanboard.com/f25/taking-league-babylon-83015/, Comment #1