Aren’t these verses very similar?
Moreover, as for me, far be it from me that I should sin against the LORD by ceasing to pray for you; but I will instruct you in the good and right way (1 Samuel 12:23).
But we will devote ourselves to prayer and to the ministry of the word (Acts 6:4).
In both verses you have spiritual leaders setting out their primary duties: prayer and instruction in truth.
Two thoughts for consideration (unrelated to each other):
First, it is interesting that Samuel sees failure to pray for those in his spiritual charge as sin.
Second, as pastors, we are typically disposed to think of the “ministry of the word” in terms of our public preaching. It is how we justify spending hours upon hours in preparation for our Sunday morning message. It is perhaps also how we justify limited contact with people.
Perhaps that is too narrow. We should think of “ministry of the word” as something that goes on in virtually every encounter with people. This does not minimize preaching and study. I think we should devote ourselves to careful study.
I would argue it maximizes the need to know the Word so that we can bring it to bear in every encounter. Studying to preach is good and necessary. Studying to converse with our neighbor, or a hurting church member, is just as necessary.