What does Genesis 21:33 mean?

In prior verses, Abraham formally accepted a covenant with Abimelech, the king of Gerar (Genesis 21:22–24). As part of this agreement, Abraham gave seven sheep to Abimelech to absolutely secure his right to a particular well. Abraham had dug this water source himself, but Abimelech's men, at some point, had taken it over (Genesis 21:25).

Having secured the ownership rights to the well at Beersheba, Abraham further puts down roots, so to speak, by planting a tamarisk tree. Tamarisk trees could reach 30 feet high and would provide excellent shade in the desert climate of the region. The planting of a tree required a reliable water source, and this further symbolizes the importance of this location.

The planting of this tree may have been related to Abraham's calling on the name of "El-Olam," the Everlasting God. Much later, Abraham's son Isaac would meet the Lord here at Beersheba and build and altar to Him. Beersheba becomes a significant spot for Israel's patriarchs and the nation.