Esomai is the future indicative first person singular of eimi (to be): 'I will be.' It supplies the future forms that the present eimi lacks. The most theologically charged use is the divine self-declaration of God to Moses in Exodus 3:12 (LXX): 'I will be [esomai] with you' — the promise of divine presence as the foundation of all mission. In Hebrews 8:10, quoting Jeremiah 31:33, God declares: 'I will be [esomai] their God, and they will be my people.'
Esomai carries eschatological weight wherever it appears as divine promise. 'I will be' reaches forward from present insufficiency into promised future reality. The covenant formula is built on the future tense of being: 'I will be your God' — not just 'I am' but 'I will be,' a promise pressed forward into time. In Revelation 21:3: 'God himself will be [estai] with them and be their God.' And in 21:7: 'I will be [esomai] their God.' The entire eschatological hope of Scripture is a divine future tense: 'I will be' — Emmanuel, God-with-us, now and forever.