Please explain joy and/or the Kimatthiyasutta
The word for joy in AN 1.11 is "pamojja":


  Pāmojja (p. 454) Pāmojja Pāmojja=pāmujja
  
  Pāmujja (p. 453) Pāmujja Pāmujja (nt.) [grd. form. tr. pa+mud, see
  similar forms under pāmokkha] delight, joy, happiness; often combd
  with pīti. -- D i.72, 196; S iii.134; iv.78=351; v.156, 398; A iii.21;
  v.1 sq., 311 sq., 339, 349; Sn 256; Nett 29; DA i.217; Sdhp 167. See
  also pāmojja.


The connection here is to the five hindrances.

From SN 46.40:


  “Bhikkhus, these five hindrances are makers of blindness, causing lack
  of vision, causing lack of knowledge, detrimental to wisdom, tending
  to vexation, leading away from Nibbāna. What five? The hindrance of
  sensual desire is a maker of blindness … The hindrance of ill will …
  The hindrance of sloth and torpor … The hindrance of restlessness and
  remorse … The hindrance of doubt is a maker of blindness … leading
  away from Nibbāna. These five hindrances are makers of blindness,
  causing lack of vision, causing lack of knowledge, detrimental to
  wisdom, tending to vexation, leading away from Nibbāna.


Ajahn Brahm commented on remorse (kukkucca) in this essay:


  Remorse refers to a specific type of restlessness which is the kammic
  effect of one's misdeeds. The only way to overcome remorse, the
  restlessness of a bad conscience, is to purify one's virtue and become
  kind, wise and gentle. It is virtually impossible for the immoral or
  the self indulgent to make deep progress in meditation.


So, basically, the purpose or virtue or ethics is to remove remorse, in such a way that it will cause the arising of joy. From joy, it goes next to rapture (piti), then tranquility (passadha) then bliss (sukha).

Piti and sukha seems to refer to jhana.

Hence, the joy arising from the removal of remorse, is basically the effect of the removal of the hindrance of remorse i.e. kukkucca (which is tied to kammic effect of one's misdeeds), by inculcating virtues. Why is it called a hindrance? It's because it hinders progress in meditation, immersion and insight.

Once the hindrance of remorse is removed, then joy results. With this joy (and the removal of all other hindrances), one can progress more easily into jhana.

There is only one small problem here. The word for remorse in AN 1.11 is "vippatisara", while the word for remorse in SN 46.40 as a hindrance is "kukkucca". But the dictionary entry for kukkucca solves this problem:


  Vippaṭisāra (p. 628) Vippaṭisāra Vippaṭisāra [vi+paṭisāra] bad
  conscience, remorse, regret, repentance Vin ii.250; D i.138; S
  iii.120, 125; iv.46; A iii.166, 197, 353; iv.69; J iv.12; v.88; Pug
  62; DhA iv.42; VvA 116; PvA 14, 60, 105, 152. -- a˚ no regret, no
  remorse A iii.46.
  
  Kukkucca (p. 218) Kukkucca Kukkucca [kud -- kicca] 1. bad doing,
  misconduct, bad character. Def. kucchitaŋ kataŋ kukataŋ tassa bhāvo
  kukkuccaŋ Vism 470 &amp; Bdhd 24; -- Various explanations in Nd2 on Sn
  1106=Dhs 1160, in its literal sense it is bad behaviour with hands and
  feet (hattha -- pada˚) J i.119=DA i.42 (in combn with ukkāsita &amp;
  khipitasadda); hattha˚ alone J ii.142. -- 2. remorse, scruple, worry.
  In this sense often with vippaṭissāra; and in conn. w. uddhacca it is
  the fourth of the five nīvaraṇas (q. v.) Vin i.49; iv.70; D i.246; S
  i.99; M i.437; A i.134=Sn 1106; A i.282; Sn 925; Nd2 379; DhA iii.483;
  iv.88; Sdhp 459; Bdhd 96. -- na kiñci k˚ŋ na koci vippaṭissāreti "has
  nobody any remorse?" S iii.120=iv.46. The dispelling of scrupulousness
  is one of the duties and virtues of a muni: k˚ŋ vinodetuŋ A v.72; k.
  pahāya D i.71=A ii.210=Pug 59; chinnakukkucca (adj.) free from remorse
  M i.108; khīṇāsava k˚ -- vūpasanta S i.167=Sn 82. -- akukkucca (adj.)
  free from worry, having no remorse Sn 850. Kukkuccaŋ kurute (c. gen.)
  to be scrupulous about J i.377; kariŋsu DhA iv.88; cp. kukkuccaŋ
  āpajjati (expl. by sankati) J iii.66.