At first Abraham lincoln said he had no purpose to meddle with slavery and then he signed the emancipation pro?

in his 1861 inaugural address Lincoln said "I have no purpose, directly or indirectly, to interfere with the institution of slavery in the States where it exists. I believe I have no lawful right to do so, and I have no inclination to do so." in september 1862 he issued his preliminary emancipation proclamation. explain why and how this marked changed of policy took place