There are two interesting points in this passage. One grammatical and one theological.
“I have loved you.” says the LORD.
This is in the perfect tense – which is the default setting of the verb in Hebrew. the Perfect tense generally indicates when an action occurs in the past that has lingering consequences in the present. In English it is different to say “I ate.” and “I have eaten.” In the simple past, “I ate”, the eating could have happened days ago so you are hungry now. In the perfect, “I have eaten” the eating was recent enough so you are in the state of being full now. However, one has to be carefull not to make too much of this, because the Hebrew verb form more or less starts in perfect (meaning completed action). It is really only significant if the verb form changes to something else. At any rate the meaning is the same – the Lord said that he has loved Israel and that love is a present reality. The translation can be “I have loved you” or “I love you.” Preserving the perfect tense force places an emphasis on the historic and enduring nature of God’s love – it is not just that at this moment.
“I have loved Jacob, but Esau I have hated.”
In context this is really talking about Judea and Edom, nations that descended from Jacob and Esau. God chose to pass his blessing down the line of Abraham, Isaac and Jacob. The idiom of “love/hate” in this context really means something like “I have loved/not loved” or “I have chosen/not chosen.” Because despite his status outside of the line of promise, Esau was not disregarded or cast aside by the Lord. The blessing of one family was not to be just for Abraham’s line only, but for all people. (Genesis 12:1-3)
Now when this is quoted in Romans 9:13, it is taken by some interpreters as referring to individual election for salvation. However, what is forgotten in the discussion is that the verse about Jacob and Esau is that its primary reference is to two Nations not two Individuals. In the context of Romans 9-11, Paul is discussing the role of Israel vis a vis the Gentiles. That is to say, it is primarily a discussion of two communities, not two individuals.
If you like the doctrine of Election or if you hate it, this passage in Romans 9 and Malachi 1 needs careful handling.