This painting is my take on the Trinity in action where Father God is the Vinedresser, God the Son is the True Vine, and the Holy Spirit is the sap within the Vine enabling the good fruit to come forth.
The Bible says that God is one, and some people wrongly take this to mean that He is one person. To believe this one would have to say for all eternity past before God created the world or anything in it, that He was turned into Himself in love since there was nothing else to love back then besides Himself, because He is love. Since God is perfect, that would mean that self-love was the greatest good back then. Since God can't improve His character, that would mean that self-love would still be the greatest good even after God created us in His own image. And that would mean that selfishness is what we all ought to aim for.
Put another way, when God created us in His own image He intended us to become like Him in our way of relating. Since God does not change, that would mean that the highest goal or objective we could have is self-love. If this were the case, then selfishness would be considered a virtue. And God could therefore not be called Love in the sense that some of us know him this day. But Jesus said that the greatest love we could have is to lay down our lives for our friends. Therefore, God can't only be one person, because if He were He would have to be a selfish God. It therefore doesn't make sense to believe in a God who is only one person.
Christianity on the other hand has rightly taught from Scripture and Tradition that God consists of three persons. Because this is so, these three persons were turned outwards towards each other in Love for all eternity (past, present, and future). This fellowship was rained on, mocked, and laughed at, on the cross. Jesus did not feel united with God the Father during His passion but He was because God can not be divided. At the cross the Trinity suffered together the ridiculing of men in order to bring men into the Trinity's holy (healthy) community. It is this kind of community that the world lacks. Followers of Jesus are commissioned to bring the life of this community to everyone by partaking of it themselves and sharing it. They are commissioned to love according to the life that is in the Trinity. The Trinity never abandons any of its persons; but they chose to become vulnerable so that they could win us back, even if that looked like God the Father abandoned Jesus, which He never would do. God was in Christ Jesus on the cross reconciling the world to Himself.