Many say that the Trinity is complex and is some regard they are right. The concept is one that baffles the mind, and some find it unbelievable. The fact that our finite minds are not able to fully grasp it is intriguing. It makes sense really because if we can fully understand the nature of God then there is a problem. Perhaps we have made a god in our own image at that point. One we can fully understand, but in the end is false and has zero ability to save. St. Augustine said that if we understand him then he is not God. St. Thomas Aquinas says that the Trinity is one and that the Father is so because of relation to the Son.
They are still one essence though they are two persons. The same can be said about the Holy Spirit. The Holy Spirit is spirated from the Father and proceeds from the Father and the Son. Spiration is to have a relation to the principle. The Father is the first principle of all creation, the Son is begotten, and the Spirit proceeds and is spirated. Spirated is a term of temporality and eternality. Thus, the Holy Spirit is eternal with no beginning or end. This is the same principle when looking at Christ as the only begotten son of God.
Christ was begotten in the temporal sense at the incarnation. In an eternal sense he is begotten because he is the love of God. He is the Word and has always existed. The Greek term for begotten is monogenes and denotes his divinity and eternality. He is the Son of God in a very different sense than a man is a father to a son. Understanding these, not only explains the Trinity in a deeper way, but shows us divine simplicity.
The work of the Trinity is ultimately a work of love. Look around at creation and you can see the beauty and majesty of the Father’s work. Something as simple as a beautiful sunset can make a lasting impression on us. In the Son we see the person of our redemption. It is awe inspiring and hard to fathom. The second person of the Trinity, the Son of God, became man. He not only became man, but was born into humble beginnings, was tempted just like us, felt the same emotions as we do, did nothing wrong, and died on the cross for our sins. In his resurrection we see the ultimate representation of hi divinity, because without the resurrection the cross meant nothing. The Holy Spirit proceeds from the Father ad Son for our help and sanctification. The three work together for one cause. That is the salvation of mankind. This entity that we cannot fully fathom love us so much.
If the Trinity is not able to be fully known is it worth trying to understand? We would not be doing our duty as Christians if we did not try to do so. We do not need minds like Augustine or Aquinas to do this. Some of us may be called to do such things, but there are many things we can do. We can read scripture, pray, and read the work of the great minds in the history of the church. We can also fully surrender ourselves to the Trinity and allow the Trinity to work through us.