1 John 5:9 If we receive the witness of men, the witness of God is greater: for this is the witness of God which he hath testified of his Son.
10 He that believeth on the Son of God hath the witness in himself: he that believeth not God hath made him a liar; because he believeth not the record that God gave of his Son.
These verses start off letting us know that we can testify about Jesus being the Son of God with all our knowledge and it still will not compare to the to God testifying about Jesus being His Son when He was baptized. Men can speak all kind of glowing reports of things Jesus has done, but when the voice comes from heaven and calls Jesus Son, it leaves no doubt who He is. Verse 10 goes on to tell us that if someone refuses the testimony of God regarding His Son, such rejection is the ultimate form of blasphemy for it is like calling God a liar. To deny that God called Jesus His Son would be the same as denying that God exist. We just need to stand firm on our belief that God said this was His Son in whom He was well pleased and we will have God alive in us.