The meaning of “stranger and sojourner” in Genesis 23:4 and Leviticus 25:23

Question

In Genesis 23:4 Abraham is in conversation with the residents of Heth and says:

"I am a stranger and a sojourner with you. Give me a possession for a burying place with you, that I may bury my dead out of my sight."
Genesis 23:4 (KJV)

The term "stranger and sojourner", ger v'toshav sounds to me like an idiomatic expression who's meaning isn't immediately evident.

• What does Abraham mean by the expression "stranger and sojourner"?
• What statement is he making about himself and his relationship with the Heth community?

It may or may not be relevant to this question, but in Leviticus 25:23 the same exact terminology, ger v'toshav is used again. There, God is describing ownership of the land of Israel and his relationship with the people of Israel:

The land shall not be sold for ever, for the land is Mine; for ye are strangers and sojourners with Me.
Leviticus 25:23 (KJV)

Edited in response to Monica's answer:

Throughout Tanakh the word ger is used to mean "resident alien," eg: Exodus 2:22, 12:49, Numbers 9:14-16 and many other places as well. How is ger v'toshav different from the type of resident alien implied by the term ger alone?

Answer 1

Rashi (Rabbi Shimon ben Yitzchak, 12th century) explains the first as meaning that Avraham is a resident alien -- not from this land but living here (even though God promised him the land at some indefinite time in the future). He is silent on the second passage. (So are the other commentaries I have to hand, beyond a general sense of "God owns the land, so we're all resident aliens", just as the verse states.)

Edit in response to the edit to the question: this Wikipedia article has a decent explanation of ger toshav. Usually in tanakh the term refers to gentiles (e.g. in discussions of their rights and Jews' obligations to them); the two passages cited in this question are unusual in applying the term to (1) a proto-Jew (Avraham) and (2) the Jewish people collectively. I don't know what significance that holds.