Translating Deuteronomy 6:4 is challenging, as there is only one verb in Hebrew. The people are to hear/listen/obey, but there are many possibilities for the translating last half of the verse. Here are a few:
The Lord is our God, the Lord is one
The Lord is our God, the Lord alone
The Lord our God is one Lord
The Lord our God is the unique Lord
The Lord our God is the only Lord
When considering the immediate context, where loving God is to infiltrate every aspect of life and to eliminate the possibility of worshipping other gods, the second translation above seems most likely. While God is certainly one and unique and the only one, the point here is not His oneness or uniqueness, but the fact that He alone is God, and that He alone is our God. As His followers, we owe our allegiance to Him alone, and to no other.
When we love the Lord with all our heart and soul and strength, we are living life differently than we would otherwise, and this is also described as fearing the Lord. Fear in the Old Testament refers to a faith relationship with God. While this can involve terror sometimes (when we sin and realize we deserve the sentence of death), that terror is dissolved by God’s grace and provision for our sin, by bearing it on Himself! Loving comes first, and it leads to obedience.
Yahweh also calls us to pass on the legacy of our relationship with God to our children or anyone we mentor. Younger people will ask us, why do you serve God? Why do you follow the Torah? This gives us the opportunity to share about our former slavery to sin, and how God is the one who saved and rescued us, and has worked many miracles on our behalf. Our testimony is the most powerful way to bring people to a saving relationship with God. Then it is clear that this is not dry doctrine or legalism, but gratitude and joy for all of God’s blessing and deliverance! In addition, obedience to God is good for us too, and leads us in paths of righteousness and life (vv. 24, 25). We are also to consider that we were the ones God brought out of Egypt, even though Moses is speaking to those who were born in the wilderness. Salvation is not because of what happened to our parents or ancestors, but it is living right now in our own hearts as well, and that is what makes it powerful and inviting and contagious.