In Psalm 13 we read this....
How long, O Lord? Will you forget me forever?
How long will you hide your face from me?
God does not forget us, and He does not hide His face from us - not ever. But David felt like God had. In this case, David's feelings and the facts were at odds with each other.
God gave us the gift of feelings, however our feelings are negatively impacted by our fallenness, and we cannot blindly trust them, or make decisions based solely on them. It wasn't wrong for David to feel these things, and most certainly it was right for him to take those feelings to God, and thankfully, he did not accept his feelings to be reality and therefore, he was able to come to the right conclusion despite his feelings....
But I have trusted in your steadfast love;
my heart shall rejoice in your salvation.
I will sing to the Lord,
because he has dealt bountifully with me.
In Psalm 14 David rightly concludes that those who reject God, intellectually or emotionally, are fools, and the result of this denial is corruption. No one on earth is naturally good, and the good we do is always tinged with evil due to the fall. But David knew that God was a refuge for His people, and that evil would not win. Though he doesn't know exactly what that deliverance will look like, he is confident it will come, and calls us to rejoice in that salvation. With the benefit of our knowledge of Christ's birth, death, and resurrection, let us rejoice in our salvation all the more!
In Psalm 15 we see a description of one who walks with God. It really is a reflection of what James talks about - not being able to separate faith and works. Our lives are a reflection of our fellowship (or lack of fellowship) with God. What does my life reflect?
In our Acts passage, Peter explains his ministry to the Gentiles, and interprets the events of our previous passages by remembering the words of Jesus, that believers would be baptized with the Holy Spirit. It was clear from both the NT and the OT, that Gentiles would come to God through the Messiah. We may sometimes be tempted to validate what someone is doing based solely on the fruit of their activity - but we also must be able to validate based on the Word of God, as Peter did.
Back in Acts 1:8 it said But you will receive power when the Holy Spirit has come upon you, and you will be my witnesses in Jerusalem and in all Judea and Samaria, and to the end of the earth.”
This verse was fulfilled because of persecution (forcing believers to spread to the ends of the earth) and the acceptance of Gentile ministry when it was validated by Peter.
Tomorrow's Bible In a Year Passage passage: Psalms 16-17; Acts 12