This is an interesting psalm and a very interesting verse. I listened to 5 sermons before coming across D.A. Carson at a UCCF conference. He chose three texts in the NT which use verse 7 Hebrews 1 v5 where it is used to teach Christ's superiority over the angels Hebrews 5 v5 where Jesus is said to meet the qualifications of a High Priest Acts 13 where the verse is put in the context of the Resurrection Carson then explains that we can take the attitude of Brodus where he says I have no idea how the OT is used but I accept it by faith without understanding it. His professor at uni took the view that the apostles played fast and loose with the OT twisting things to suit them and we need to accept that and get over it. Lastly he suggests there is a coherent hermeneutic that explains this. (It was at this point I checked my bookcase and realised that he was the coauthor of the hefty tome "The NT use of the OT") It is this latter third option that Carson goes on to explain, which I am currently struggling to compass.