For as the Father has life in himself, so he has granted the Son also to have life in himself.
How do trinitarians explain the fact that the Father has granted life to the Son?
The "begetting" here is understood in an eternal sense, and is not a matter of being made or created. The creeds phrase it as eternally begetting (fathering), or pretemporal begetting, or an eternal proceeding from. And they are explicit in that it is not a matter of being made or created.
From the Athanasian Creed,
And from the Nicene Creed,
The Son proceeds from The Father and is therefore of the same eternal substance. This differs from created entities, which are different in "substance" from their creator. The Father is the eternal cause of the Son; but the Son is not created or a distinct substance from the Father. The Father and the Son, with the Holy Spirit, are one in being.
All Scripture is quoted from the New Revised King James Version
you are confusing the material with the immaterial. The Trinity (God) is Deity. And in :
What Jesus is saying is that the father has given *his physical body*life within itself. That is why Jesus said:
John 10:17 and 18
Jesus life, death, and resurrection, were all commanded by God the father.
Where your confusion comes in is that you unconsciously attribute materialistic properties to God. We must understand that God is something beyond the intelligence of man.
We will never completely know God until we meet him face to face.
I would read it as "Has authorised the Son to have life in Himself"....Whilst the Persons of the Holy Trinity are each God in essence, yet they are separate Persons with various things they do. So the Father sent the Son and the Son took to Himself a human nature (thus Jesus Christ is two natures in one person). But it was not the Father or the Holy Spirit Who took on a human nature, only the Son. We might say that in the Trinity, the Father authorised the Son to become a man and in perfect eternal harmony, the three agreed that it should be so. Likewise that the Father should send the Son and after the resurrection of the Lord, that they should send the Holy Spirit at Pentecost to indwell believers. Also see Matthew Henry's comments about this.
For a further explanantion of the Trinity pls see What is the doctrine of the Trinity?