There are many spiritual benefits from receiving the Eucharist on a regular basis, and one of those benefits is the strengthening of our soul, that we may more easily resist the allure of future sins.
St. Thomas Aquinas explains this effect of the sacrament in his Summa Theologiae by first framing the objection.
It seems that man is not preserved by this sacrament from future sins. For there are many that receive this sacrament worthily, who afterwards fall into sin. Now this would not happen if this sacrament were to preserve them from future sins. Consequently, it is not an effect of this sacrament to preserve from future sins.
This is a very rational argument, as we experience this ourselves whenever we receive Holy Communion and then continue on our life of sin.
However, St. Thomas Aquinas explains why this reality shouldn't distract us from the reality of God's grace given to us.
[T]his sacrament preserves man from sin ... For, first of all, by uniting man with Christ through grace, it strengthens his spiritual life, as spiritual food and spiritual medicine, according to Psalm 103:5: "(That) bread strengthens [Vulgate: 'may strengthen'] man's heart." Augustine likewise says (Tract. xxvi in Joan.): "Approach without fear; it is bread, not poison." Secondly, inasmuch as it is a sign of Christ's Passion, whereby the devils are conquered, it repels all the assaults of demons. Hence Chrysostom says (Hom. xlvi in Joan.): "Like lions breathing forth fire, thus do we depart from that table, being made terrible to the devil."
At the same time, the key to preventing future sins is contingent on the person's openness to God's grace.
The effect of this sacrament is received according to man's condition: such is the case with every active cause in that its effect is received in matter according to the condition of the matter. But such is the condition of man on earth that his free-will can be bent to good or evil. Hence, although this sacrament of itself has the power of preserving from sin, yet it does not take away from man the possibility of sinning.
If we receive the Eucharist in a state of sin, closed-off from God's grace, then we will likely continue sinning for the foreseeable future.
However, if we are open and receive God's grace with our whole heart, God will help us in our time of need, protecting us from future temptations.
