this is because the disbelievers have followed falsehood and the believers have followed the truth from their lord. thus god explains to the human being their own prospects.
ذلك بأن الذين كفروا اتبعوا الباطل وأن الذين آمنوا اتبعوا الحق من ربهم كذلك يضرب الله للناس أمثالهم