13 Because I go to the Father: and whatsoever you shall ask the Father in my name, that will I do: that the Father may be glorified in the Son. 14 If you shall ask me any thing in my name, that I will do.
it does say in John 14:13-14 that prayer to God MUST be said through Jesus.
Right. It would therefore be wrong to utter a prayer like this: "Mary, please cure my disease" or "Mary, please forgive me my sins". Luckily, I know of no one who prays to Mary like that, at the exclusion of Jesus. The whole idea to pray to Mary is after all based on the fact of her proximity to Jesus as His mother. But it is perfectly fine, in the light of these verses, to ask Mary to join me in praying to Jesus for these things.
Here, for example, St. Paul instructs St. Timothy to offer intercession to God in Timothy's church:
1 I desire therefore, first of all, that supplications, prayers, intercessions, and thanksgivings be made for all men: 2 For kings, and for all that are in high station: that we may lead a quiet and a peaceable life in all piety and chastity. 3 For this is good and acceptable in the sight of God our Saviour, 4 Who will have all men to be saved, and to come to the knowledge of the truth. 5 For there is one God, and one mediator of God and men, the man Christ Jesus: 6 Who gave himself a redemption for all(1 Tim. 2)
See how St. Paul acknowledges in the same passage that Jesus is the sole mediator to God, yet that Timothy should pray and intercede for salvation of others.
What Bible verse is that?