We do know that because that is what the Bible tells us...that is if we are capable of using our power of reasoning on the scriptures...oh, and if you know your Hebrew and Greek...
The physical structure of a human or an animal. The Hebrew word
gewi·yahʹ refers to a body, whether alive (
Ge 47:18) or dead. (
1Sa 31:10; Ps 110:6) The Hebrew
neve·lahʹ comes from the root verb
na·velʹ (“wither”;
Ps 1:3) and is variously rendered “dead body,” ‘carcass,’ and “corpse.” (
Le 5:2; De 14:8; Isa 26:19)
Ba·sarʹ, the Hebrew word for flesh, can represent the whole body. (Compare
Ps 16:9; see
FLESH.) The usual Greek word for “body” is
soʹma (
Mt 5:29), but
khros, literally “skin,” is rendered “body” in
Acts 19:12. The Greek word
ptoʹma, which comes from the root verb
piʹpto (fall), refers to a fallen body or “corpse.” (
Mt 14:12) The different kinds of physical bodies are composed of different kinds of flesh, together with the life-force.—
1Co 15:39; Jas 2:26; Ge 7:22
While there are physical bodies, visible and palpable, there are also spiritual bodies, invisible to human eyes and entirely beyond human senses. (
1Co 15:44) The bodies of spirit persons (God, Christ, the angels) are glorious. “At no time has anyone beheld God.” (
1Jo 4:12) Man cannot see God and live. (
Ex 33:20) When the apostle Paul had only a glimpse of the manifestation of Jesus Christ after Jesus’ resurrection, he fell to the ground and was blinded by the brilliance, a miracle being required to restore his sight. (
Ac 9:3-5, 17, 18; 26:13, 14) Likewise, angels are far more powerful than men. (
2Pe 2:11) They are glorious, brilliant ones and have appeared as such in physical manifestations. (
Mt 28:2-4; Lu 2:9) These spirit sons of God have vision strong enough to see and endure the brilliance of the Almighty God.—
Lu 1:19.
https://wol.jw.org/en/wol/d/r1/lp-e/1200000783