Who is God?
This question has been around since the beginning of time, and finding out its answer is one of the key issues of life. According to the Bible (God's revealed truth about Himself) there is only one God (Deut. 6:4) who exists in three co-equal and eternal persons. In other words, we worship "God" (singular), who exists as three persons: the Father, Son, and Holy Spirit (plural). This is a very difficult concept to understand, but the Bible makes it clear that this concept of a "Trinity" is the essential nature of God (in other words, who God is). Some have described the Trinity like a hot iron. In a hot iron, you have light, heat, and metal. Light, heat, and metal are three different elements that form one coherent item. But there is really no way to describe the Trinity accurately with an earthly illustration-why? Because we're trying to describe an eternal God from a human perspective. That's sort of like a group of monkeys trying to describe nuclear physics. Belief in the Trinity comes down to a faith issue: we believe in the Trinity, not because we can comprehend one God who exists as three co-equal persons, but because the Bible makes it clear that it is truth.
There are many religions that do not believe in the Trinity. Jehovah Witnesses - Mormons and Muslims just to name a few. But the Bible is clear. There is only one God (Deut. 6:4) who exists as three persons. (John 6:27, Ephesians 4:6, Hebrews 1:8, Acts 5:3-4 - these passages show the Father, Son, and Holy Spirit as being God). If we deny the truth of the Trinity, then we deny the truth of Scripture. If we deny the truth of Scripture, then how are we to believe what the Bible claims about salvation? This is why it is key to understand God as Trinity.
The entire Trinity is at work all the time in the world, the church, and in our own spiritual life. For instance, when we pray, the Father listens to our prayers (Matthew 7:7-11), the Son is our "defense attorney" before the Father in case we have done anything wrong (I John 2:1), and the Spirit intercedes on our behalf so that our prayers are heard with maximum effect by the Father (Romans 8:26,27.) The entire Trinity is involved, not only in our prayer lives, but also in our salvation (when we trusted Christ as our Savior), our sanctification (our spiritual growth) and our glorification (when we are transformed into our glorified bodies after we die). The Father, Son and Holy Spirit are always working in us and on us!
