I'd like to get a better understanding of the difference between these two sentences:
1) He has just come.
2) He came just now.
Hello, Rasha—Apart from the obvious grammatical difference (present perfect versus simple past), there is very little difference in meaning between those two sentences. The closest comparison between pairs like these:
(1a) He's just come.
(1b) He just came.
(2a) I've just washed the dishes.
(2b) I just washed the dishes.
(3a) She's just won a gold medal.
(3b) She just won a gold medal.
The difference in meaning between the two sentences in each pair is so subtle that it would be possible for someone to challenge whether the hair-splitting difference even matters.
That said, I would say that, although both the (a) sentences and the (b) sentences indicate a recent happening, the (a) sentences do so in a way that expresses lively, present relevance, whereas the (b) sentences are just matter-of-fact.
I would be more inclined to use the (a) sentences if I were announcing something that were relevant to the situation calling for the utterance, or if I wanted to put something in a slightly more formal way. Otherwise, I'd use the (b) sentences.
