Yes, soul can choose to sin, (Gn. 4:7) and do, but no one can come to God unless drawn by Him, (Jn. 6:44) and granted repentance unto life (Acts 11:18) by Him who convicts of sin, (Jn. 16:8) and opens hearts, and gives heart-purifying regenerating faith. (Eph. 2:8,9; Acts 10:43; 15:7-9) And who works to chasten wayward believers unto repentance so they will not be condemned with the world, (1 Co. 11:32) and warns the same against departing from the faith. (Heb. 3:12; 10:25-39; Gal. 5:1-4)
Which effectual faith is imputed for righteousness, (Rm. 4:5) and is set in contrast to any system of justification on the basis of meriting salvation and or actually becoming good enough to be with God. (Galatians 3:21; Titus 3:5) Which is what your Roman false gospel effectively teaches.
As Jesus told us in John 6:53 “unless you eat the flesh of the Son of Man and drink his blood, you have no life in you;” (Eucharist -eternal life).
Thus the question must be asked again and which RCs like yourself refuse to answer, which is if taking part in the Lord's supper is essential to obtain spiritual life, just as other "verily, verily" statements such as Jn. 3:3 are, then how can faithful Prots who reject Catholic transubstantiation be part of the body of Christ?
But contrary to the Catholic contrivance of the Lord's supper (see link), nowhere in the only wholly inspired-of-God and substantive record of what the NT church believed, which is Acts thru Revelation (which best shows how they understood the OT and the gospels) is the Lord's supper described as spiritual food, and the means of obtaining spiritual life in oneself. Instead, and consistent with the metaphorical use of eating and drinking, the word of God is what is called spiritual "milk," (1Co. 3:22; 1Pt. 1:22) and "meat," (Heb. 5:12-14) what is said to "nourish" the souls of believers, and believing it is how the lost obtain life in themselves. (1 Timothy 4:6; Acts 15:7-9; cf. Psalms 19:7) Thus the primary active function of pastors is preaching, (1 Timothy 4:2) by which they “feed the flock” (Acts 20:28; 1Pt. 5:2)
Righteousness is a gift because we are made righteous in Christ apart from circumcision and observance of the Torah. Forgiveness is an essential part of justification.
“So it will be at the close of the age.The angels will come out and separate the evil from the righteous.” Matthew 13:49
Through graces given freely by God one can accept God or reject God.
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Christ’s death and resurrection merited justification for all. We accept and receive justification through Baptism and becoming friends of God. We can lose that friendship through mortal sin and regain the friendship through the Sacrament of Reconciliation (Confession).
Your question: “Thus the question must be asked again and which RCs like yourself refuse to answer, which is if taking part in the Lord’s supper is essential to obtain spiritual life, just as other “verily, verily” statements such as Jn. 3:3 are, then how can faithful Prots who reject Catholic transubstantiation be part of the body of Christ?”
I question if there are faithful protestants (you are entitled to believe what you want) as I believe that protestants are not following Christ’s teachings but the opinions of man. The words of Jesus is clearly stated in John 6 and the readings about the Last Supper. Jesus shared the Eucharist at Emmaus (Luke 24:30).
I do believe in the great Mercy of Jesus. It s Christ that will pass judgement when we die. I am also concerned that many Catholics (including some in leadership) are not following Christ’s teachings. We should not leave Christ’s Church because of sinners. As Jesus told us “For I came not to call the righteous, but the sinners.” Matthew 9:13I believe that Christ will be a just judge.
Jesus gave us the Sacraments of Baptism, Eucharist and Confession through His Catholic Church as necessary for our salvation.
The Catholic Church teaches:
Christ asserted the necessity of faith and Baptism and affirmed at the same time the necessity of the Church. Mark 16:15 and John 3:5 Matthew 12:30 and 18:17
“Basing itself on Scripture and Tradition, the Council teaches that the Church, a pilgrim now on earth, is necessary for salvation: the one Christ is the mediator and the way of salvation; he is present to us in his body which is the Church. He himself explicitly asserted the necessity of faith and Baptism, and thereby affirmed at the same time the necessity of the Church which men enter through Baptism as through a door. Hence they could not be saved who, knowing that the Catholic Church was founded as necessary by God through Christ, would refuse either to enter it or to remain in it” (CCC here quotes The Dogmatic Constitution on the Church, “Lumen Gentium,” 14, from the documents of Vatican II).
Ignatius of Antioch
“I have no taste for corruptible food nor for the pleasures of this life. I desire the bread of God, which is the flesh of Jesus Christ . . . and for drink I desire his blood, which is love incorruptible” (Letter to the Romans 7:3 [A.D. 110]).
Irenaeus
“If the Lord were from other than the Father, how could he rightly take bread, which is of the same creation as our own, and confess it to be his body and affirm that the mixture in the cup is his blood?” (Against Heresies 4:33–32 [A.D. 189]).
https://www.catholic.com/tract/the-real-presence
Priests act especially in the person of Christ as ministers of holy things, particularly in the Sacrifice of the Mass, the sacrifice of Christ who gave himself for the sanctification of men. Vatican II
The Blessed Mother of God has asked us to pray the Rosary for the conversion of sinners.