After Mr. Douglas had taken ground against Mr. Buchanan’s administration relative to the so-called Lecompton Constitution of Kansas, and had received the indorsement of the Democratic party of Illinois--his re-election as Senator depending upon the result of the State election in 1858--the Republican Convention of that year with shouts of applause, unanimously resolved that Abraham Lincoln was “the first and only choice of the Republicans of Illinois for the United States Senate, as the successor of Stephen A. Douglas.” At the close of the proceedings, he delivered the following speech, which struck the key-note of his contest with Senator Douglas, one of the most exciting and remarkable ever witnessed in this country: “GENTLEMEN OF THE CONVENTION:--If we could first know where we are, and whither we are tending, we could then better judge what to do, and how to do it. We are now far on into the fifth year, since a policy was initiated, with the avowed object, and confident promise of putting an end to slavery agitation. Under the operation of that policy, that agitation had not only not ceased, but has constantly augmented. In my opinion, it will not cease, until a crisis shall have been reached, and passed. ‘A house divided against itself can not stand.’ I believe this Government can not endure, permanently, half slave and half free. I do not expect the Union to be dissolved--I do not expect the house to fall--but I do expect it will cease to be divided. It will become all one thing, or all the other. Either the opponents of slavery will arrest the further spread of it, and place it where the public mind shall rest in the belief that it is in course of ultimate extinction, or its advocates will push it forward, till it shall become alike lawful in all the States, old as well as new--North as well as South. “Have we no tendency to the latter condition? Let any one who doubts, carefully contemplate that now almost complete legal combination--piece of machinery, so to speak--compounded of the Nebraska doctrine, and the Dred Scott decision. Let him consider not only what work the machinery is adapted to do, and how well adapted, but also let him study the history of its construction, and trace, if he can, or rather fail, if he can, to trace the evidences of design, and concert of action, among its chief master-workers from the beginning. “But, so far, Congress only had acted; and an indorsement by the people, real or apparent, was indispensable, to save the point already gained, and give chance for more. The new year of 1854 found slavery excluded from more than half the States by State Constitutions, and from most of the national territory by Congressional prohibition. Four days later commenced the struggle, which ended in repealing that Congressional prohibition. This opened all the national territory to slavery, and was the first point gained.