Mark 12:29
This is the Shema from Deuteronomy 6:4. The Jews knew it well, and it is a foundation of the Jewish way of life and thinking. Jesus, being Jewish himself, did not leave this off of the commandment for several reasons.
For one, the Jews would have found it quite offensive I am sure. It seemed more complete and respectful to say the whole thing. Also, Jesus is not in the habit of shortening the Scripture to save time like we are today. We tend to shorten the Lord’s words and embellish our own.
The Shema establishes the oneness of Almighty God. Of course many say this is inconsistent with the doctrine of the Trinity. However, to deny the reality of the Trinity, you have to do some mighty heavy cutting out of things, both in the Old and New Testament. In the New, you have to change much of the story and teachings of Christ. In the Old, you have to disregard plurals used to refer to God and interpret away any hints at the compound oneness of the Godhead. The Spirit of God, the Lord, and the LORD, all have to be exactly the same. Or you have to come up with some sort of artificial delineation.
Heavenly Father, the truth is what makes you so wonderful! We see over and over how that you have made everything well. You are One indeed. There is no disagreement in you. You are perfectly balanced at all times. There is no separation or disunity in you. And through Christ, we have fellowship with you in your glory. Thank you! In the name of the Lord Jesus Christ I pray and praise you, Amen.