Yes, he highlighted the departure from the faith of Christianity also known as the Apostasy.
Strong's definition:
G646 apostasia
ap-os-tas-ee'-ah
Feminine of the same as G647;
defection from truth (properly the state), (“apostasy”) : - falling away, forsake.
Total KJV occurrences: 2
Thayer's Definition:
G646 apostasia
1)
a falling away, defection, apostasy
Part of Speech: noun feminine
A Related Word by Thayer’s/Strong’s Number: feminine of the same as G647
Citing in TDNT: 1:513, 88
Total KJV occurrences: 2
Abbott-Smith Manual Greek Lexicon of the New Testament:
Apostasia
defection, apostasy, revolt; in late Gk. (MM, Exp., viii; Lft., Notes, 111; Cremer, 308) for cl. ?p?stas?? , freq. in sense of political revolt, in LXX (e.g. Joshua 22:22, 2 Chronicles 29:19, Jeremiah 2:19)
and NT always of religious apostasy: Ac21:21, II Th 2:3.
Liddell and Scott:
A defection, revolt, v.l. in D.H.7.1, J.Vit.10, Plu.Galb.1; esp.
in religious sense, rebellion against God, apostasy, LXX Jo.22.22, 2 Ep.
Th.2.3 .
Liddell, Scott, Jones Ancient Greek Lexicon (LSJ):
apostasia
I
a departure from one's religion, apostasy , Salv. Gub. Dei, 6, p. 128; Aug. c. Jul. 56.
apostasia apostasiae N F ::
apostasy, departure from one's religion, repudiation of one's faith
Winer's Grammar:
Apostasia,
a falling away, defection, apostasy; in the Bible namely, from the true religion: Acts 21:21; 2 Thessalonians 2:3 ; ((Joshua 22:22; 2 Chronicles 29:19; 2 Chronicles 33:19); Jeremiah 2:19; Jeremiah 36

29 ) 32 Complutensian; 1 Macc. 2:15). The earlier Greeks say Apostasis; see Lob. ad Phryn., p. 528; (Winer's Grammar, 24).
greeklexicon.org (Greek-English lexicon):
G646 apostasia
Part(s) of speech: Noun, Feminine
Definition:
defection, apostasy, revolt.