Deuteronomy 4:23-26 includes both an injunction to do right and a threat of retribution for failure to do right. Such a warning of impending negative reinforcement is always intended to stir fear in the heart of the subject, thereby producing obedience. Through Moses, God started His motivational speech with intimidation.
Comparatively, Deuteronomy 4:37-40 contains both an order to obey and a promise of reward for said submission. Such a guarantee of eventual positive reinforcement is always intended to stir up an emotional connection in the heart of a subordinate... again, thereby producing obedience. Through Moses, God concluded His coaching discourse with inspiration.
Now, here is the sad part. How successful was this approach in the long run? Initially, the admixture of intimidation and inspiration worked rather well. The Jews did fine during the duration of Joshua’s tenure... but, within a generation they were guilty of wholesale defection from the straight and narrow way. They forsook God, His love and His law. Not surprisingly, God had anticipated that they would turn from Him, so He instructed them to pass all of His words along to their posterity (Deuteronomy 4 :9-10) and to teach them, that, even in judgment, if they would repent, then there would be mercy that could be obtained (Deuteronomy 4:29-31).
God repeatedly squeezed the people with both kindness and revenge (Deuteronomy 4:3-4). But in the end, the only sufficient cure for them... or for us... was and is substitutional atonement by Immanuel. Of course, even in that, we find potential positive and negative reinforcement motivations - namely, heaven and hell.