There's a lot to be said about the two versions of Gates of Paradise, the first (for Children) and the second (For the Sexes). This first study is not exactly an introduction but a personal thesis re the relationship between Father and Son.
One important source for this work is Symbol and Image in William Blake by G.W.Digby and secondly my own intuition.
Aged Ignorance suggests an old father faced with a young son. To you men how often have you 'put the screws' on you boy because you felt like he was not 'living up to snuff'; and as a boy how often have your wanted to crush the old man?
In Vain-glory hatcht & nurst By double Spectres Self Accurst My Son! my Son! thou treatest me But as I have instructed thee
And proceeds with these lines:
In Aged Ignorance profound Holy & cold I clipd the Wings Of all Sublunary Things
And in depths of my Dungeons Closed the Father & the Sons(Erdman 268)
But the story ends with this happy outcome: But when once I did descry The Immortal Man that cannot Die Thro evening shades I haste away To close the Labours of my Day
The text here is based on the distress King David went through with his son Absolum:
2nd Samuel 19.4:
"The king covered his face and cried aloud, "O my son Absalom! O Absalom, my son, my son!"
(Read the chapter and find out about what was happening.)