The form esti (ἐστί, also written ἐστίν) is the third person singular present indicative of eimi — meaning "is, it is, he/she/it is." It is one of the most frequently occurring words in the Greek NT, appearing hundreds of times. In the mouth of Jesus, its theological weight is staggering — particularly in the seven great "I AM" (ἐγώ εἰμι) declarations of John's Gospel.
When Jesus declares "I am the bread of life" (John 6:35), "I am the resurrection and the life" (John 11:25), "I am the way, the truth, and the life" (John 14:6) — the predicate nominative following eimi defines the very nature of Christ. John's Gospel opens with the same verb form reaching back to eternity: "In the beginning was [ἦν] the Word... and the Word was God." The present tense esti grounds eternal realities in the present moment. Christ's lordship is not past or future — it is, now.