The secret lies in a total offering of self, withholding nothing. Jesus was a total oblation on the Cross. There wasn't a cell of His body or sentiment of His heart that He didn't offer to the Father. Anything we withhold for ourselves is lost, because we only possess what we give.
St Francis of Assisi who, because of the elevated fervor of his devotion to the Eucharist can be considered a special guide on the topic, ends his wonderful discourse on the Eucharist with this exhortation: "Look at God's humility, my brothers, and pour out your hearts before Him. Humble yourselves, so that He who has given Himself wholly to you may receive you wholly."
In the Imitation of Christ, Jesus says: "Look, I offered Myself wholly to the Father for you; I also gave My whole body and blood for food, that I might be wholly yours, and you should remain mine. But if you stand upon yourself and do not offer yourself freely to My will, the offering is not fully made, nor will union between us be complete."
What we hold back for ourselves to keep a margin of freedom from God pollutes all the rest. It is the little silk thread
of the Cross speaks of, which prevents the bird from flying. St John
Fr Raniero Cantalamessa
The Eucharist, Our Sanctification