1. What does gen 6:4 means?

Naphilim refers to a powerful race of giants. propably 9-10 feet tall. These have been the same mention in Numbers 13:33. Goliath in the case whom David killed was 9 feet tall (1 Sam 17). Sons of God - Refers to descendant from Seth and Daughters of man refers to Cain's evil descendants. Naphilim use their physical advantage to oppress the people around them.

2. Gen7 :21- underwater creatures were not destroyed ?

YES. They would have survive. So there will be chances of great fish (bigger than whale??) like the one that swallow a prophet. Do you know his name?

3. Gen 8:7 - why send both raven and dove? what is the difference? why raven did not return means got dry land but when dove is send yet say the land is not dry?

Noah sends out the birds raven and dove. Raven keep flying to and fro until water dried up from the earth. Dove send out and water still cover the surface of the earth.

So there is different degree of dryness. The dove was sent 3 times: first cannot find any place to set foot. Second return in the evening with a freshly plucked olive leaf. Meaning trees being growth in the land. The third and final time, the dove did not return.

One saying mention that the raven feed on carcass of dead animals one of the cursed/unclean bird yet the Dove with the olive represents the symbol of the Holy Spirit.

4: Gen 11:1, 10:31 , 5 ,20 - thought they already have different language? why say they only have 1 language?

In Gen 10:25 Son of Eber are Peleg and Joktan and in Peleg time the earth was divided. So from Peleg and Joktan there is a division. One line to Abraham another line the one that builds Babylon. Tower of Babel is mostly a Ziggurat, a common structure in Babylonia at this time. They build it for their name sake. Gen 11 explains how the different language comes about. Gen 10 is genealogies. So from here think God confuses the 1 language to many. Now through the Holy Spirit, what did God gave to reverse that?

5. Gen 6: 3- thought God decided to give people 120 yrs of age y many born after this still live up to 600 years?

It takes time for that to take effect. Remember when Adam and Eve ate the fruit from the tree of knowledge of good and evil they did not immediately died. God also is a just and merciful God giving the people in the days of Noah time to repent of their sinful ways. It takes a long time for the Ark to be build and don't you think his neighbor will see it and ask him what is it for? Now I know that no one man could live beyond 120 years old.

6: Job 1: 6 - 12 - why does God want to entertain satan , a not so cute character?

Satan is previously an arch angel whose role is leading worship before pride and sin enters him. He is the accuser so that is how is accuses the saints before God. God did not entertain his accusation. How I see it, is God point Job to Satan, but God is in full control of the whole situation and since God is Omniscient Omnipresence and Omnipower. God can be present with Job when he was tested and God has the power to do anything to help if need and God is already all knowing and knew the outcome. At the end of it, Job know God better after the whole process. Job proves that Satan was wrong.

7. Job 1:6 - why satan can be among them? thought he is banished?

He is still a created being and have been there to serve God till he was banished. Yet he still possess the same quality of an angel just that he is a fallen one. One thing to consider if truly evil and holiness cannot be in the same place and God is a Merciful and Just God, we all would have died, with Holy Spirit living in us a not so holy house of God. Plus God paid the Just price for us to receive Jesus righteousness so that we will not die in his presence and will not be banished like Adam and Eve.