Genesis 1:1-3
1 In the beginning God created the heavens and the earth. 2 The earth was without form, and void; and darkness was on the face of the deep. And the Spirit of God was hovering over the face of the waters. 3 Then God said...
Right in the first three verses of the Bible, we can learn something very important about the nature of God: He is one and yet more than one.
This fact will become more obvious in the New Testament, but the Old Testament writers, who had not yet received light on that matter from Jesus, may not have understood this aspect of God's nature as fully as we, in hindsight, can.
Still, inspiration led them (whether they were aware of it or not), to leave hints, even in the Old Testament, that God is a unit of three, and Moses alluded to that fact here as well.
In verse 1, "God" is mentioned, followed by "Spirit of God" in verse 2, but the last (and arguably most important) mention, is in verse 3, "God said".
More than four thousand years after the week of creation, the apostle John would begin his gospel with these famous three verses:
1 In the beginning was the Word, and the Word was with God, and the Word was God. 2 He was in the beginning with God. 3 All things were made through Him, and without Him nothing was made that was made.
We later learn in his book that he is referring to Jesus. Jesus is "the Word", He is the "God said". When Jesus speaks, what He says, becomes reality. In fact, (I think that) most of the miracles that Jesus is recorded in the gospels to have performed, He brought about simply by speaking.
Jesus was present during that first week described in the first chapter of Genesis, and had (in some sense that I won't speculate about) a special role to play in the creation of the world: He spoke the earth and its wildlife into existence.
However, if it wasn't clear enough that God is more than one, Moses then quoted God in verse 26 directly:
Then God said, "Let Us make man..."
Emphasis mine.
Why is this important?
In I John 4:8 the apostle John states that "God is love".
This is to say, God is love, and love is God. They are synonyms. Love is not just one of God's many characteristics. Love is what God fundamentally is. It's a simple description, the depth of which cannot exhausted.
Yet, for God to be love, God could not be one individual.
Why?
God is eternal. He "from everlasting to everlasting" (Psalm 90:2). This means that He has always existed, even before He created the earth. That would have been a very long time to be by Himself, but He wasn't.
God the Father, God the Son, and God the Holy Spirit (all of which are titles that we attribute to the three persons, but don't denote an order of conception or anything like that), have always been with each other. They have always experienced love, either in giving it, receiving it, or deferring it (observing the other two experiencing a loving relationship).
So as God is more than one, and God is love, He likewise created us to form families and/or communities, where we all can, hopefully, experience giving love, receiving love, and deferring love (observe others love each other).
This is (among other reasons) why God created us in His "image" (Genesis 1:26).