Here is my attempt at answering these questions:
What is the meaning of “set thine house in order”?
It means prepare to meet your maker, and have everything ready for your family (or kingdom, in this case) to move forward with as little difficulty as possible.
Did Isaiah already know that Hezekiah wasn’t going to die?
Isaiah fully trusted in God, and he didn’t need any advanced warning about God’s intentions. He simply listened with his spiritual sense, and acted as he was directed. Also, if Hezekiah’s reaction had been different, the verdict may have remained unchanged.
Did Isaiah tell him that he was going to die in order that Hezekiah would repent and pray to the Lord? Why on the third day?
Not too long ago in a Roundtable it was mentioned — in essence — that just because someone (prophet, doctor, anyone) tells you that you are going to die, it does not make it true. Divine Life is our only lawmaker. So I feel that Mrs. Eddy’s words on page 66 of Science and Health speak to why Hezekiah needed to be told he would die: “Trials teach mortals not to lean on a material staff, — a broken reed, which pierces the heart. We do not half remember this in the sunshine of joy and prosperity. Sorrow is salutary. Through great tribulation we enter the kingdom. Trials are proofs of God’s care.” Salutary is defined in part as “contributing to some beneficial purpose.” (1828 Webster’s Dictionary)
It seems that Hezekiah was very blessed and that his prayer blessed all his people.
Hezekiah’s blessing was remembering that he serves God alone, and that his complete trust must be in Truth, Life, and Love. And, since “whatever blesses one blesses all” (S&H, p. 206), Hezekiah’s blessing became his kindgom’s blessing.
Does the lump of figs has an special meaning?
I take using the lump of figs to simple mean ‘being obedient.’ Isaiah knew, as Mary Baker Eddy has taught us, that matter has no power to heal or do anything. Isaiah also knew that Hezekiah would still “lean on a material staff.” That is why Hezekiah needed spiritual sense to come through Isaiah, and why he needed signs and wonders from God. To truly trust God at times feels like this stanza from Hymn 169:
“Lead, kindly Light, amid the encircling gloom,
Lead Thou me on;
The night is dark, and I am far from home,
Lead Thou me on.
Keep Thou my feet; I do not ask to see
The distant scene; one step enough for me.”
Thank you!