Hi Antaiwan,
Gen 6:5 Then Yahweh saw that great, was the wickedness of man in the earth, and that, every purpose of the devices of His heart, was only wicked all the day;
v. 6 and it grieved Yahweh, that He had made man in the earth,—and He took sorrow unto His heart. (Rotherham)
God is lamenting over what He sees happening, even though He knew it would happen and He does not regret it, because this is how God's plan was suppose to go. God is full of love for His creation and He does not enjoy watching the process that is being worked out here.
Jesus one time spoke how He would like to gather up all of Jerusalem and protect them like a mother hen, and yes He knew that was not God's plan.
Mat 23:37 Jerusalem! Jerusalem! that slayeth the prophets, and stoneth them that have been sent unto her,—how often, would I have gathered thy children, like as a hen gathereth her chickens under her wings,—and ye would not!
Then in verse 7 God is now saying what must happen as part of His plan.
Gen 6:7 And Yahweh said—I must wipe off man whom I created from off the face of the ground, from man unto beast unto creeping thing, and unto the bird of the heavens,—for I am grieved that I made them.
Sometimes I go to a movie and I know it's a story about something terrible that has happened and will be sad, even thought I know what is suppose to happen, I still am overcome with sadness and tears when I watch it happen.
God does not enjoy seeing all this evil and suffering of mankind here on earth, but His plan calls for it and the ultimate good it will bring.
Eze 33:11 Say to them: "As I live,' says the Lord GOD, "I have no pleasure in the death of the wicked, but that the wicked turn from his way and live. Turn, turn from your evil ways! For why should you die, O house of Israel?'
Num 23:19 GOD is, not a man, that He should lie, Nor a son of Adam, that He should repent,—Hath, he, said, and will not perform? Yea spoken, and will not make it stand fast?
In this verse it says "God is not a man," and then it shows one way He is not like man "that He should lie." And it continues by saying "Nor a son of Adam," and then it says how "that He should repent." The word "repent" is directed towards a particular thing "a son of Adam," that's all of mankind, that have sinned and are in need of repentance. But God has no need to repent, like mankind!
So this is just giving reference to ways God is not like a man.
Rom 3:23 For all have sinned, and come short of the glory of God;
2Pe 3:9 The Lord is not slack concerning His promise, as some count slackness, but is longsuffering toward us, not willing that any should perish but that all should come to repentance.
1Co 15:22 For as in Adam all die, even so in Christ all shall be made alive.
Hope this helps
mercy, peace and love
Kat