What specific language in the Emancipation Proclamation indicates that the freeing of slaves is partly for military reasons

The specific language is ‘Moreover, the Proclamation announced the acceptance of black men into the Union army and Navy enabling the liberated to become liberators’.

This is gotten from the excerpt which explains the main reason why the slaves were freed. They were freed for partly military reasons as they were integrated into the Union Army and Navy to strengthen the military system during the war.