We use bread and wine, and make the active step of taking it in. And that active step, done in this setting, with the readings and prayers, and with the fellowship of brothers and sisters in the faith, actually makes us spiritually vulnerable. It pries open the avenue to our heart. The Holy Spirit then travels that avenue, and does his inner, mysterious work, pulling us closer to Jesus, like a lover embracing the beloved so that the one spirit, His Spirit, rules in him and in us. Not physically, of course.
Bread remains bread.
The juice remains a grape product. But we DO take Christ in. For while we handle, taste and swallow these very ordinary elements, the Holy Spirit moves around them and us, enters us, and touches our Spirit. Perhaps it sounds all very mystical and unearthly. Communion is a time that goes beyond our heads.