Hebrews 5:5
"So also Christ glorified not himself to be made a high priest but he that said unto him, Thou art my Son, this day have I begotten thee."
Now we're going to go back once again where we were earlier in Psalms chapter 2 because in case someone missed the last program we want you to understand what Paul is referring to. That God the Father designated to God the Son that He should be a high priest but not in the lineage of Aaron, the humanly priesthood, but it's going to be the priesthood according to Melchizedek and we'll see that a little later in this half-hour.
Psalms 2:7
"I will declare the decree: the LORD (here of course, the Lord is a reference to God the Father) hath said unto me, (the Son) thou art my Son; (and remember it's capitalized so we're speaking here of Christ way back - 1000 BC.) this day have I begotten thee."
Now let's turn all the way up to Acts chapter 13 and find out what that meant when God said "this day I have begotten thee." I pointed out, I think, in the last program, David wrote the Psalms around 1000 BC but that's not when Christ became the only begotten Son of God - but prophecy-wise, that was when it was spoken. But in Acts chapter 13, we have the Scriptural definition of what it meant to be the only begotten Son of God.