Is it true that ONLY the Holy Spirit can give a person the faith that the Eucharist is TRULY the Body, Blood, Soul and Divinity of Christ?
Yes. All faith and virtue arrives in us by means of the Holy Spirit alone. To believe even in God, to say a prayer, is complete reliance on the Holy Spirit. So similarly, faith in Eucharisit can only be given by the Holy Spirit. We, however, are called to be open to the spirit, and pray that he would give us the faith we need for these things.