Imam al-Safarini (1114-1188 AH) stated:
أَهْلُ السُّنَّةِ وَالْجَمَاعَةِ ثَلَاثُ فِرَقٍ الْأَثَرِيَّةُ وَإِمَامُهُمْ أَحْمَدُ بْنُ حَنْبَلٍ رَضِيَ اللَّهُ عَنْهُ وَالْأَشْعَرِيَّةُ وَإِمَامُهُمْ أَبُو الْحَسَنِ الْأَشْعَرِيُّ رَحِمَهُ اللَّهُ وَالْمَاتُرِيدِيَّةُ وَإِمَامُهُمْ أَبُو مَنْصُورٍ الْمَاتُرِيدِيُّ.
Translation: “Ahl al-sunnah wa’l-jama‘ah is three groups: Atharis, whose leader is Ahmad b. Hanbal, may Allah be pleased with him; Ash‘aris, whose leader is Abu’l-Hasan al-Ash‘ari, may Allah have mercy on him; and Maturidis, whose leader is Abu Mansur al-Maturidi.”
If there is only one saved sect, then how can there be different schools of fiqh and aqida? Well these represent the valid disagreements (ikhtilaf) between the scholars of these schools of fiqh and aqida.
After the rise of the Ash’ari and Maturidi school, one would be hard pressed to find a jurist (faqih), hadith scholar, exegete (mufassir), or grammarian who wasn’t of these two schools. Most scholars in Islamic history were Ash’aris or Maturidis.
Historically, Hanafis have mostly been Maturidis, Malikis and Shafi’is have mostly been Ash’aris, and Hanbalis have mostly been Atharis.