For a believing Catholic with habitual or Mortal sin on their conscience , that pew can be a pretty lonely place at Communion time. Quite a while back, I remember having to frequently refrain from receiving Communion while fulfilling my Sunday obligation because of sin. It went on for several years and more often than not I was refraining … and the pew was never a comfortable seat at Communion time. You might say I was buying a little more kleenex at that time (;)) .
A person is still fed with God’s Word in the first part of the Mass.
It might be helpful to try looking at the second part (the Liturgy of the Eucharist) this way when one is obliged to refrain from Holy Communion:
First of all, it is possible that perhaps not everyone else who is going up to receive Holy Communion may be properly disposed to do so. Thank God for your conscience.
One side of the coin is that , because of sin, you are prevented from receiving Holy Communion. The other side of that same coin should be that you believe that Jesus is personally present in the Eucharist … otherwise the first side of the coin makes no sense. In this light, refraining from reception of Holy Communion because of the state of one’s soul can be seen as an act of respect towards the True Presence.
In the Eucharistic Prayer, ranking directly after the words of consecration, the next most important words repeated are “we offer”.
So either in your heart (I used to ask my guardian angel to do it) place this act of faith - of respect/belief in Jesus about to become present in the Eucharist, on the paten so that Jesus may offer this together with the priest and the faithful to God the Father … and I used to make sure that I placed all the sadness, the hurt, of not being able to receive Holy Communion on the paten too.
Remember that the Sacrifice of Calvary is made present for us again (re-presented) at the Mass … the foot of the Cross is a great place to beg for favors.
Too many of us are unaware that a person can still bring very much to offer God at Mass - even when they are obliged to refrain from receiving Holy Communion (that “sadness” and “hurt” part is a big one). If a person does this, the opportunity to receive the sacrament of Reconciliation will likely be made more available ( I think of it as The Father running to embrace the prodigal son “while he was still far off”).
I’ve personally found the Rosary to be of immense help to overcome certain sins with God’s grace. Now, I’m at a point where I need to attend daily Mass for my life to make any sense at all. But occasionally, on certain days , the priority is still to first seek the sacrament of Reconciliation .
Mortal sin is God’s /the Church’s way of telling us that something we are doing or that some type of lifestyle is harmful to our souls.
(… just my own limited opinion above).