One of these promises is conditional, while the other is unconditional.
» Unconditional promise: "I will tear the kingdom out of the hand of Solomon and will give ten tribes to you" (verse 31). God goes on to explain that He will leave one tribe, Judah, under the Davidic monarchy in order "that My servant David may always have a lamp before Me in Jerusalem" (verse 36). God did this to honor His promise to David that He would "establish the throne of [Solomon's] kingdom forever" (II Samuel 7:12-13). Christ, the last King, descended from Judah and will sit on that throne forever.
» Conditional promise: ". . . if you heed all that I command you, walk in My ways, and do what is right in My sight, to keep My statutes and My commandments, as My servant David did, then I will be with you and build for you an enduring house, as I built for David, and will give Israel to you" (I Kings 11:38). This is a remarkable promise. God says He will establish in Jeroboam a permanent dynasty over ten tribes if he keeps His covenant.