Zechariah 12 - “the Spirit of grace and of supplication”, What does that mean?

Zec 12:10
"And I will pour out on the house of David and on the inhabitants of Jerusalem, the Spirit of grace and of supplication, so that they will look on Me whom they have pierced; and they will mourn for Him, as one mourns for an only son, and they will weep bitterly over Him, like the bitter weeping over a first-born.

Elohim will pour out the Spirit of grace and of supplication on the inhabitants of Jerusalem. When He does this, they will understand His Word.

Prov. 1:23 “Turn to my reproof, Behold, I will pour out my spirit on you; I will make my words known to you.

Isa. 44:3-5 ‘For I will pour out water on the thirsty land And streams on the dry ground; I will pour out My Spirit on your offspring, And My blessing on your descendants; 4And they will spring up among the grass Like poplars by streams of water.’ 5“This one will say, ‘I am the LORD’S’; And that one will call on the name of Jacob; And another will write on his hand, ‘Belonging to the LORD,’ And will name Israel’s name with honor.

Isa. 59:19-21 So they will fear the name of the LORD from the west And His glory from the rising of the sun, For He will come like a rushing stream, Which the wind of the LORD drives. 20“And a Redeemer will come to Zion, And to those who turn from transgression in Jacob,” declares the LORD. 21“And as for Me, this is My covenant with them,” says the LORD: “My Spirit which is upon you, and My words which I have put in your mouth, shall not depart from your mouth, nor from the mouth of your offspring, nor from the mouth of your offspring’s offspring,” says the LORD, “from now and forever.”

When He pours His Spirit upon them and they understand His Word, they will look upon "Me" whom they have pierced and they will mourn for Him.

Psalm 22:16-17 For dogs have surrounded me; A band of evildoers has encompassed me; They pierced my hands and my feet. 17I can count all my bones. They look, they stare at me;

Rev. 1:7 BEHOLD, HE IS COMING WITH THE CLOUDS, and every eye will see Him, even those who pierced Him; and all the tribes of the earth will mourn over Him. Even so. Amen.

Amos 8:9-10 “And it will come about in that day,” declares the Lord GOD, “That I shall make the sun go down at noon And make the earth dark in broad daylight. 10“Then I shall turn your festivals into mourning And all your songs into lamentation; And I will bring sackcloth on everyone’s loins And baldness on every head. And I will make it like a time of mourning for an only son, And the end of it will be like a bitter day.

Matt. 24:29-31 “But immediately after the tribulation of those days THE SUN WILL BE DARKENED, AND THE MOON WILL NOT GIVE ITS LIGHT, AND THE STARS WILL FALL from the sky, and the powers of the heavens will be shaken, 30and then the sign of the Son of Man will appear in the sky, and then all the tribes of the earth will mourn, and they will see the SON OF MAN COMING ON THE CLOUDS OF THE SKY with power and great glory. 31“And He will send forth His angels with A GREAT TRUMPET and THEY WILL GATHER TOGETHER His elect from the four winds, from one end of the sky to the other.