It is the Holy Spirit that unites us to God. When we are totally Spirit-filled, we become one with God. This union breaks down all barriers between you and God and between you and all the saints in heaven or others on earth who are in union with the Lord, creating perfect unity. That's why I feel I already know all the saints in heaven whom I have not even met. That's why the best marriage on earth is one between a man and a woman who are both in complete union with God. But no matter, we can always seek to attain union with the Lord himself. Believe in the Lord completely, receive the body and blood in the Holy Eucharist with utmost devotion, and ask to be filled with the Holy Spirit, and you become one with the Lord.