Interesting is the thought of this topic. While the word 'trinity' isn't found in scripture the meaning of the word is nonetheless shouted from the Bible's pages. Akin to the wind, although invisible the Holy Trinity's existence to me is indisputable..
In the above verse from Romans 11:33 there is emphasis not only on the vast immeasureable wisdom and knowledge of God but also that mankind is profoundly limited.
Man has to deal with man's math.... 1+1=2...
God is not limited with man's math... 1 man and 1 woman for example = 3 with his blessing in Holy Matrimony.
Skeptics may be consumed with reason and stubbornly point out that 1+1+1 = 3. The same reasoning can be said also 1x1x1=1.
Proverbs 21:30 There is no wisdom nor understanding nor counsel against the Lord.
Man's carnal ability will never overcome the above reminder from Romans 11:33 'past finding out' wisdom and knowledge of God.
While there are those who would twist, omit and even rewrite the Word it does not alter the fact of the original truth from God's Word.
2 Peter 1:16 For we have not followed cunningly devised fables, when we made known unto you the power and coming of our Lord Jesus Christ, but were eyewitnesses of his majesty.
I choose today to take the Word of God without any reservations. As a trusting child hops into an automobile with a loving parent to a happy birthday party not at all understanding the mechanics of that vehicle to get them there.... I too trust and believe Jesus my Lord and Savior yet not understanding all the mechanics at His disposal to get me to Heaven. In spite of my limited knowledge I believe He will get me there.
Following are only a few of many scriptures supporting the Holy Trinity.
Matthew 3:16 And Jesus, when he was baptized, went up straightway out of the water: and, lo, the heavens were opened unto him, and he saw the Spirit of God descending like a dove, and lighting upon him:17 And lo a voice from heaven, saying, This is my beloved Son, in whom I am well pleased.
The following two verses are Matthew's very last written in his gospel. No huge endeavor is made to delve into the existence of the Holy Trinity. Merely the author is exhorting simple instruction with his parting words and yet out of simplicity the Trinity is affirmed.
Matthew 28:19 Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost:20 Teaching them to observe all things whatsoever I have commanded you: and, lo, I am with you always, even unto the end of the world. Amen.
John 14:26 But the Comforter, which is the Holy Ghost, whom the Father will send in my name, he shall teach you all things, and bring all things to your remembrance, whatsoever I have said unto you.
1 John 5:7
For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one.
When topically discussing and contemplating the Holy Trinity with people from all walks of life, men and women passionate with their own beliefs and satisfied in agreed upon conclusions that admittedly does draw some grounds for debate and controvery. Heated debate to include sharp confrontation and even dissention. I believe it is at this point Satan is most victorious, when peoples, whole denominations differ sharply away from Jesus, the Word made flesh, John 1:14. Jesus is the Bible.
Similar to Matthew's parting words the following verse is from Timothy's first letter. He readily acknowledges the room for controversy but instead of parting words being argumentive Timothy takes the high road leaving no room for dissention and simply associates the word 'mystery' with the Trinity.
1 Timothy 3:16 And without controversy great is the mystery of godliness: God was manifest in the flesh, justified in the Spirit, seen of angels, preached unto the Gentiles, believed on in the world, received up into glory.