In hindsight, maybe Moses was on to something back in Exodus 3-4 when he told God he wasn’t right for the job. Of course, we know that he eventually became right for the job, but his original excuses had at least some weight to them.
He wasn’t special (Exodus 3:11).
He didn’t have authority by himself (Exodus 3:13).
The people didn’t listen to him (Exodus 4:1).
He wasn’t eloquent (Exodus 4:10).
At times, he didn’t really enjoy the job (Exodus 4:13).
The Moses we see in Deuteronomy 1 is just as honest. He’s tired, overworked, old, and even more importantly, realistic as to his own weaknesses. Twice in the span of five verses (Deuteronomy 1:8-12), he tells the people that he “can not bear the burden of the people alone.”
Who can blame him? According to population estimates, Israel would have been well over two million people (including women and children). That’s way too much for one man to take upon himself; he even admits that he put judges in charge of the people to lighten the load (Deuteronomy 1:13-16).
These judges were chosen by the people. Since there were judges appointed over groups of thousands, hundreds, fifties and tens, it’s possible that the number of these men totaled well into the thousands. That’s way more than Moses knew personally; they had to be appointed by the people.
In this way, Moses tells the people through that sentence that while he personally led them as a whole, the real day-to-day leadership came from their trusted overseers. Those people weren’t going anywhere (until they were eventually replaced).
Moses’ humility in this chapter has a purpose. He wants them to know that the reason they made it to Canaan had virtually nothing to do with his own strength. The real strength came from God’s leadership, enacted by the practical leadership of the people.
The specific phrasing in this Text seems to bear this idea out. The literal translation of Deuteronomy 1:9 has Moses saying “I cannot carry you by myself,” which means that he is not physically or emotionally capable of taking them all the way to Canaan.
Whether Moses means that because (a) he’s about to die or (b) he’s only a man is irrelevant. The point is that he’s only one man—God is the real source of strength. Though he may die, everything will continue on.
And God isn’t limited by death or capability. Moses prays that the Lord will increase them “a thousand-fold more than [they] are.” He can handle it!
Deuteronomy is seen as Moses’ final farewell, and while this early section can read as a complaint, realistically, it’s about ensuring a safe transition of power. Death shouldn’t slow Israel down, because death can’t touch God. He’ll stay with them long after Moses is gone.