Cases: dative

which gave us: date: April 1, 2005 (= given day)
which gave us: data (= information given)

	He gives food to the slave. (= to him)	σῖτον παρέχει τῷ δούλῳ
	Take food (fertilizer e.g.) to the tree. (= to it)	φέρε σῖτον τῷ δένδρῳ

It is also the got-for-whom case:

I bought this Πέτρῳ (for him, for Peter.)

In English it would be called: indirect object.

Peter kicks the ball to Josh. (Peter connects directly with the ball. But the connection between Peter and Josh is indirect, via the ball. )
Peter buys an icecream for his sister. (The connection Peter - sister is indirect, via the ice-cream, which is bought directly.)
Peter says to Lucy: I love you. (Peter communicates with Lucy via those words he says, so Lucy is the indirect object, she is not said, she is spoken to).

So why do we say: ὁ αὐτουργὸς καλεῖ τὸν δοῦλον,
      accusative (direct object) and not dative (indirect object)?

Because the farmer calls his slave directly.
We are not interested in the words he might say,
   but in the action itself: calling, and the direct object directly called: the slave.

Whereas he says to him means that he says words to him: he communicates with him by means of those words which he says to him.

ὁ αὐτουργὸς λέγει τῷ δούλῳ · ἐλθὲ δεῦρο.

But the dative, like the other cases (genitive and accusative) is also used after certain prepositions. Especially those indicating position where things/people are, rest, sit, work, live, dwell etc..

• lesson 1a
  ἐν ταῖς Ἀθήναις
  ἐν τοῖς ἀγροῖς
• lesson 1b
  ἐν τῷ ἀγρῷ
  ὑπὸ τῷ δένδρῳ
• lesson 2a
  ἐν τῷ οἴκῳ