[Q3. Psalm 139]

No hiding here, there is nothing that God dows not know, in this case about the Psalmist, for he is the creation of God.

David wants complete purity and prays that God will totally cleanse him of all sin.

[Q2. Psalm 19]

To me it seems a bit like Show and Tell

It seems that the first 6 verses mean that God wants us to see Him. He is the Artist, the Master Sculptor, His is the Creation and the awesomeness of it all has inspired David to acknowledge the magnificence and beauty and to give God the Glory. The sun in this artistic masterpiece is the ruling image as it is ever present and everywhere and even if you can't see it...it is felt, it is heat and it is vital to life.

So after the see comes tell and it is all about the Word of God you cannot see it...you can, if tuned in and desirous, feel it and benefit from the heat of the Word which is essential/vital to living a Godly life. David wants this perfect life aligned to God, wants to make the right choices, wants forgiveness, cleansing of his soul through the Word of God.

It would appear to me that David is a bit concerned that maybe past/present mistakes might forfeit his chances of deliverance. He wants everything behind so he can be thoroughly cleansed and live his life as he knows God wants him to. You just can't hear the Word and do nothing...you have to hear it, understand it and follow through.

The mind and the mouth, his thought and speech, his meditations of his heart he needs to be acceptable to God and he prays for that. He wants to be overhauled, to allow the Word to inspire change and be effective in becoming like Christ.

[Q1. Psalm 8]

I am not biblically inclined so please bear with me in my responses

Psalm 8 means to me in my reading and understanding:

That God is the Creator, the Very Top, The Ultimate, The Supreme Being