“We should live in such a manner as to be able to receive Holy Communion every day.” – St. Augustine
My Jesus, I believe that you are present in the Most Blessed Sacrament. I love you above all things, and I desire to receive you into my soul. Since I cannot now receive you sacramentally, come at least spiritually into my heart. As though you were already there, I embrace you and unite myself wholly to you. Never permit me to be separated from you. Amen. (St. Alphonsus Liguori)
Commentary [Fish Eaters]: We are obliged to attend Mass each Sunday and every other Holy Day of Obligation. Sometimes, though, we just can't be there. One's own sickness or the obligations to care for a sick person, having given birth within the past 6 weeks, dangerous weather (and other safety hazards), not being able to find a way there - life happens. There is no guilt in missing Mass if the circumstances are out of one's control (mortal sin always requires not only grave matter and knowledge, but consent of the will).
The rule of thumb concerning Mass availability is that if one is required to travel more than an hour to reach a Mass, one is not guilty of sin by not attending. Nor is one obliged to attend if the only Masses available are offered by formal schismatics or those who mix heresy into the liturgy. If a liturgy is scandalous, heretical, or simply not Catholic, one is obligated to not attend even if it goes by the label "Catholic." We must be especially wary of taking our children to liturgies that pose a danger to their eternal souls by the priest's watering down the Faith, making the Sacrifice seem unimportant, engaging in behaviors that confuse or are Protestantized, etc. (for this reason, many traditional Catholics are "home-aloners" - unable to attend Mass in their area and having to make do with the spiritual Communion this page describes).
...Sometimes, too, we just crave Communion with our Eucharistic Lord but have already received Him sacramentally that day.
In all these instances, we are encouraged to make what is known as a "spiritual Communion," an act expressing what was described by St. Thomas Aquinas as "an ardent desire to receive Jesus in the Most Holy Sacrament and in lovingly embracing Him." In a spiritual Communion, we, with contrite, humble hearts, ask our Lord to come to us in the same way He would if we were able to receive the Sacrament. This can be done as often as one likes, informally in one's own words or through one of the traditional prayers which appear [above].
What is the value of this practice? The graces received may be as great as - or greater than - those received by some people in the actual Sacrament. Though, of course, the Sacrament itself is inherently greater, our disposition toward the Sacrament affect whether and how we receive its fruits. For example, imagine a woman who is unable to be with her husband but who desires him as contrasted with a woman who has her husband's presence but doesn't care for him. Which husband would be more apt to pour out his love for his wife?
St. Leonard of Port-Maurice offers this advice for receiving Spiritual Communion: In order to facilitate a practice of such great excellence, ponder what I have to say. When the priest is about to give himself Communion in holy Mass, do you, keeping composed externally and internally, excite in your heart an act of true contrition, and humbly striking your breast, in token that you acknowledge yourself unworthy of so great a grace, make all those acts of love, of self-surrender, of humility, and the rest, which you are accustomed to make when you communicate sacramentally, and then desire with a lively longing to receive your good Jesus, veiled in the sacrament for your benefit. And to kindle your devotion, imagine that most holy Mary, or some saint, your holy advocate, is holding forth to you the sacred particle; figure yourself receiving it, and then, embracing Jesus in your heart, reply to Him, over and over again, with interior words prompted by love: “Come, Jesus, my Beloved, come within this my poor heart; come and satiate my desires; come and sanctify my soul; come, most sweet Jesus, come!” This said, be still; contemplate your good God within you, and, as if you really had communicated, adore Him, thank Him, and perform all those interior acts to which you are accustomed after sacramental Communion.