Genesis 21:33 And Abraham planted a grove in Beer-Sheba, and called there on the name of the Lord, the everlasting God.
After God led Abraham to make a peace covenant with Abimelech in Beer-Sheba, he settled there and staked a claim to the Land of Promise. Though he did not yet see the promise of land fulfilled, he believed the promise of the Lord that his descendants would live in the Land and receive their inheritance. He set aside a place to call on the name of the Lord. He believed The Eternal God, worshiped Him for who He is, and thanked Him for His Covenant Promise.
He saw by faith what he could not yet see by sight. He responded with thanks for a promise, though he did not yet see the fulfillment, the reality (or realty), of it. The promise itself was real enough. The gift of faith makes it real, and it just as true and present as the thing promised. ”Faith is the substance of things hoped for, the evidence of things not seen [Hebrews 11:1].”
In fact, he believed for more than just physical land: ”He looked for a city which hath foundations, whose builder and maker is God [11:10].” Abraham saw what John saw in Revelation 21 and 22. He did not receive the promises, ”but having seen them afar off…embraced them [11:13].”
We respond likewise. We call on the name of the Lord in faith, worship, and thanks. By faith we already have what we do not yet see. Therefore we call.