In the poem, "The Convergence of the Twain", published in 1915, and commemorating the sinking of the luxury ocean liner Titanic three years before, Thomas Hardy gives free reign to his deterministic view of reality. Thus, after mocking the pride and vanity of the 'unsinkable' ship in the first six stanzas of the 11-stanza poem, in the seventh Hardy avers that it was an "Immanent Will that...prepared a sinister mate for her...A Shape of Ice" (lines 18-21), referring, of course, to the iceberg which - sitting across the sealane - sent the Titanic to the bottom of the North Atlantic with a loss of 1200 persons; significantly, mention of this is missing from the poem. In these lines Hardy reveals his creed, if it can be called that. His 'god' is an impersonal, dispassionate "Immanent Will", capitalized in the poem to show its implacable power. Hardy later employs a synonym for it - calling it "the Spinner of the Years (line 31) - thus, bringing his view closer to the Fates of Greek mythology, those three sisters who spun out the inescapable threads of destiny. As Titanic took shape, so Hardy's thesis goes, "in shadowy silent distance grew the Iceberg too", until the 'twain' encountered one another in their predestined, ill-fated collision. Reinforcing his view that no beneficent Mind governs the universe, Hardy depicts the destruction of Titanic, identified as she, by the iceberg, qualified mostly with male terms, as a kind of violation, using such words as “ravish”, “mate”, “intimate welding”, and “consummation”. Finally, a sadness pervades the poem, but especially in last five stanzas. It is not a sadness over the loss of life, but over the realization that one is trapped in a meaningless universe, the plaything of forces frighteningly real, but unseen, like the hidden bulk of an iceberg.
the basic answer is that the 'imminent will' is some kind of Godly force/a God ect. it is deliberately vague because Thomas Hardy himself never 'found' whether God was true. he wanted to believe in God (see capitalisation of 'Imminent will' in Convergence of the Twain and 'blessed Hope' in The Darkling Thrush) but advancing science made him believe there is no God.
one deeper interpretation, is that Hardy is blaming human 'vanity' and obsession with 'mirrors meant to glass the opulent' for needing nature/a god to punish them. try and find some emotive language in the poem that provokes sorrow at so many people dying - zero if any! this is because Hardy isn't concentrating on the human tragedy (he could even be saying that we, as humans, deserved it). even the title uses scientific diction 'convergence'.
on the other hand, look at the structure of the poem. 3 line stanzas, 11 stanzas - unusual, isn't it? it makes the poem feel cut short, reflecting they way that human lives and the expectation of new technology within the Titanic were cut short. this could therefore be hardy expressing sorrow/regret at what has happened, saying the imminent will causing the crash was uncalled for, not inevitable,
thats just a couple of interpretations but i hope they helps!