The below is at the end of Augustine’s great work on the Trinity. It is the quintessential bringing together of piety and theology. In fact it is the mind of a truly great theologian as he brings together exegetical theology, systematic theology, apologetics, and practical theology.
O Lord our God, we believe in you, Father and Son and Holy Spirit. Truth would not have said, Go and baptize the nations in the name of the Father and of the Son and of the Holy Spirit (Mt 28:19), unless you were a triad. Nor would you have commanded us to be baptized, Lord God, in the name of any who is not Lord God. Nor would it have been said with divine authority, Hear O Israel, the Lord your God is one God (Dt 6:4), unless while being a triad you were still one Lord God. And if you, God and Father, were yourself also the Son your Word Jesus Christ, were yourself also your gift the Holy Spirit, we would not read in the documents of truth God sent his Son (Gal 4:4), nor would you, only-begotten one, have said of the Holy Spirit, whom the father will send in my name (Jn 14:26), and, whom I will send you from the Father (Jn 15:26). Directing my attention toward this rule of faith as best I could, as far as you enable me to, I have sought you and desired intellectually what I have believed, and I have argued much and toiled much. O Lord my God, my one hope, listen to me lest out of weariness I should stop wanting to seek you, but let me seek your face always, and with ardor. Do you yourself give me the strength to seek, having caused yourself to be found and having given me the hope of finding you more and more. Before you lies my strength and weakness; preserve the one, heal the other. Before you lies my knowledge and my ignorance; where you have opened to me, receive me as I come in; where you have shut to me, open to me as I knock. Let me remember you, let me understand you, let me love you. Increase these things in me until you refashion me entirely.
St. Augustine, On the Trinity, New City Press, 436.
I appeal to you, brothers, to watch out for those who cause divisions and create obstacles contrary to the doctrine that you have been taught; avoid them. For such persons do not serve our Lord Christ, but their own appetites, and by smooth talk and flattery they deceive the hearts of the naïve. (Romans 16:17-18)