When David wrote this, he didn't know what scientists would later find out with their technology about the seas and the dry land rising out of the water and there being more water than there is land. The importance of a person with clean hands and a pure heart as one who ascends standing in His holy place. Even if we are saved by grace alone, the Christian life should characterize us as having clean hands and a pure heart. Anything other than that does a lot of damage to people's perceptions of the Church of God!
Why is Jacob mentioned here in the other psalms? If God can accept Jacob and make something of him, He can do the same with you and me. Now we have the King of Glory mentioned as entering here. I believe this is none other than our Lord Jesus Christ as he rides out of Heaven on a white war horse in revelation 19:11 and all the redeemed army with Him. he will take control in due time. Paul called him the Lord of Glory in I Corinthians 2:8. I will be there with him when that happens. Will you?