How do we know the Trinity doctrine is true?

The truth of the Trinity is substantiated through various scriptures that demonstrate the roles and essence of each person. For instance, Isaiah 45:5 affirms that there is one God, while Genesis 1:26 reveals the let 'us' in creating mankind, indicating a plurality within the divine nature. Additionally, John 14:17 illustrates the personhood of the Holy Spirit, further validating this doctrine. The consistent portrayal of God's oneness alongside the distinct persons helps solidify the understanding that while God is one, He exists in three co-equal persons.