1 Chronicles 19:12
And he said, If the Syrians be too strong for me, then thou shalt help me: but if the children of Ammon be too strong for thee, then I will help thee. And he said, If the Syrians be too strong for me, then thou shalt help me: but if the children of Ammon be too strong for thee, then I will help thee.
The verse belongs to the war against the Syrians and the Ammonites, whose opposing forces were divided. Joab led Israel's men against the Syrians, while Abishai led the rest of the army against the Ammonites. They made a pact of mutual help for the two fronts, that if the Syrians proved too strong for Joab then Abishai would help him, and if the children of Ammon proved too strong for Abishai then Joab would help him, so their defense was coordinated. In that setting they encouraged each other to be courageous and to fight for their people and for their cities.