We can infer the oneness of God from the creation of the universe, because the universe is a work connected together as one thing from beginning to end, all dependent on one God as the body depends on its soul. The universe was designed to allow God to be omnipresent, keep every detail of it under his supervision, and maintain it perpetually as one entity, that is, preserve it. This is why Jehovah God says he is “the First and the Last, the Beginning and the End, the Alpha and the Omega” (see Isaiah 44:6; Revelation 1:8, 17); and why he says elsewhere that he makes all things, stretches out the heavens, and extends the earth by himself (see Isaiah 44:24).
This vast system called the universe is a work connected as one thing from beginning to end because God had a single purpose in creating it: an angelic heaven populated by the human race. All the things that make up the world are means of fulfilling that purpose, because someone who intends an end result also intends the means to achieve it.
If we view this world as a work containing the means of fulfilling the aforementioned purpose, we can see the created universe as a work connected together into one thing; and see that this world is a complex structure of useful functions arranged and prioritized for the sake of the human race, the source of the angelic heaven.
Divine love cannot intend anything other than that people should forever have the blessings of its divineness. Divine wisdom cannot produce anything other than useful things that are means of fulfilling that purpose.
Upon examining the world with this universal idea in mind, every wise person is capable of grasping that there is one Creator of the universe and that his essence is love and wisdom. For this reason every single thing in this world is of benefit to us; if it seems of no direct benefit, at least it is of indirect benefit. The fruits of the earth and the animals benefit us with food and also with clothing.
from True Christianity, Volume 1, Section 13