How was the incarnation an act of solidarity?

In Christian theology, the incarnation is when God came to earth in human form, as a human infant. God was born as Jesus, the son of Mary. Although made of the "same substance" as God, not a "creature" like other humans, Jesus did at the same time become a real human person who was born and who grew, lived, suffered, and died before being resurrected.
The incarnation was an act of solidarity because it brought together God and human beings. They were united in and through the body of Jesus Christ because Jesus was both wholly human and wholly divine. Jesus, according to Christian theology, models for humans how to be divine in our human form. We can do this by believing in Jesus, which means willingly following in his footsteps by acting with love, joy, peace, compassion, forgiveness, and mercy. This behavior makes us fully human/humane, which, in turn, makes us divine and grants us eternal life. We don't have to do this perfectly because God's grace saves us. However, the idea is that Christ-like behavior reflects the divine.
The incarnation also led to the trinity, which can be understood as the three faces of the one God: God the father (the creator, who is all-mighty and all-knowing), God the son (Jesus Christ, God in human form) and the Holy Spirit, the invisible spirit of God poured on the earth (Jesus called this spirit the Counselor in John 15:26). These three facets of God exist in solidarity in what is called the perichoresis, the dance or relationship of three equal parts.