Psalm 77 tells us that remembering God's help in the past gives us courage, strength, and hope to continue in present trouble.
Psalm 78 is a lesson in history. We need to learn from our past mistakes, and even the past mistakes of others, so we do not simply repeat them in our own lives.
In our Acts passage we see again God's sovereignty and man's responsibility.
God had a plan, but that plan came to pass through the warnings and urgings of Paul, through the actions of the Centurion and his men, and through the urgings of Paul and the obedience of the folk on board. In each case it is clear that without the steps that were taken -- to keep the sailors from escaping and to convince the people to eat -- the plan would not have come to pass. Paul says so explicitly in v. 31 and it is implied in his remark in v. 34 that they "need the food to survive."
But this is an exact parallel of the matter of salvation itself. There is a divine plan: he has a chosen people, their salvation is certain, their names are in the book of life, Christ will raise them to life at the last day.
But, at the same time, there are means appointed to secure their salvation: the work of Christ, the work of his Spirit in them, and their own believing, repenting, obeying, and persevering.
Tomorrow's Bible In a Year Passage passage: Psalms 79-80; Acts 28