Bible Gateway:
https://www.biblegateway.com/passage/?search=Psalm+16&version=AMP

Bible Hub:
https://biblehub.com/commentaries/psalms/16-8.htm
MacLaren's Expositions:
I. First, then, life here may be God’s presence with us, to make us steadfast.

Mark the Psalmist’s language. ‘I have set the Lord always in front of me-before my face.’ Emphasis is placed on ‘set’ and ‘always.’ God is ever by our sides, but we may be very far away from Him, ‘though He be not far off from every one of us,’ and if we are to have Him blazing, clear and unobscured above and beyond all the mists and hubbub of earth, we shall need continual effort in order to keep Him in our sight. ‘I have set the Lord’-He permits me to put out my hand, as it were, and station Him where I want Him, that I may always have Him in my sight, and be able to look at Him and be calm and blessed.

You cannot do that, if you let the world, and wealth, and business, and anxieties, and ambitions, and cares, and sorrows, and duties, and family responsibilities, jostle and hustle Him out of your minds and hearts. You cannot do it if, like John Bunyan’s man with the muckrake, you keep your eyes always down on the straw at your feet, and never lift them to the crown above. How many men in Manchester (any city in the world) walk its streets from year’s end to year’s end, and never look up to the sky except to see whether they must take their umbrellas with them or not? And so all the magnificence and beauty of the daily heavens, and the nightly gemming of the empty places with perpetually burning stars, are lost to them! So, God is blazing there in front of us,

BUT unless we set ourselves to it, we shall never see Him. You have to look, by a conscious effort, over and away from the things that are ‘seen and temporal’ if you want to see the things that are ‘Unseen and Eternal.’