Famously, the Sadducees denied the concept of life after death (cf. Mt. 22.23; Acts 23.8). This was partially due to the fact that they accepted as authoritative only the first five books of the Old Testament, which did not address the afterlife — or so they supposed.
Jesus charged them with being in error for failing to understand the Scriptures (Mt. 22.29).
Exodus 3.6, which he quotes — and which the Sadducees themselves accepted — proves the resurrection doctrine. It reads:
“I am the God of Abraham, the God of Isaac, and the God of Jacob.”
God spoke these words to Moses at the burning bush, hundreds of years after those three men had died. Yet, Jesus stresses the present tense form — I am. He does not say, “I was the God of Abraham…” — as if Abraham is now wholly gone, no longer able to accept God as his God.
Hence, Abraham, Isaac, and Jacob were then living, even though their bodies had been decaying for centuries. He concludes: “God is not the God of dead-ones, but of the living” (Mt. 22.32). There is life after death!
In your own studies of the Scriptures, pay attention to the verb tenses. As Jesus demonstrates, that information can prove useful to gain a fuller knowledge of the Scriptures; it may even serve well to establish and/or disprove an entire belief-system or doctrine.
Truly, the tense matters!