Believing in the Eucharist and believing in the Lord Jesus are not at odds with each other.
Scripture says to believe in the Lord Jesus Christ. There is no emphasis on believing in the Eucharist other than some reference Jesus had said to the Jews only because they did not believe Him earlier on how they were to receive this living bread and that was by coming to & believing in Jesus Christ. John 6:33-35
John 14:15 "If you love me, you will keep my commandments."
That saying was in relation to the promise of the permanent indwelling Holy Ghost and if you go back to the first verse, you will see that commandmet repeated on down to verse 15 which is to believe Him.
John 15:20 "If they kept my word, they will also keep yours."
Catholics tend to have an all-of-the-above approach to the words of the New Testament.
No, they do not, especially when they took His words that was spoken to unbelieving Jews to build their false teachings on and not on what He has said earlier in John 6:33-35 or even when He explained to His disciples afterwards that the "flesh" in the eating thereof profits nothing as it is His words as believing in Him is life.
The Mass is actually saying that God the Son's sacrifice for sin is the only thing that's going to prevent us from rotting separated from God for all eternity. All of God's actions are eternal. The Eucharist is not a new sacrifice of Christ. It is the same eternal sacrifice re-presented (not represented) on the altar.
I know it is not a new sacrifice in one regards, but it is new if it is continual as being present at that altar again for that sacrifice again.
If the RCC really believes there is no continual sacrifice for sins, then the Mass would cease to exist, but because the RCC does, then that sacrifice as happening at that moment for a Catholic to partake again is akin to saying that the one before that wasn't good enough and thus insulting to God in every way possible.
Hebrews 10:26 For if we sin wilfully after that we have received the knowledge of the truth, there remaineth no more sacrifice for sins,
That means after having knowledge of the truth that there is no more sacrifice for sins, and yet partake of the Eucharist in the Mass, then that is sinning willfully.
Hebrews 10:27 But a certain fearful looking for of judgment and fiery indignation, which shall devour the adversaries. 28 He that despised Moses' law died without mercy under two or three witnesses: 29 Of how much sorer punishment, suppose ye, shall he be thought worthy, who hath trodden under foot the Son of God, and hath counted the blood of the covenant, wherewith he was sanctified, an unholy thing, and hath done despite unto the Spirit of grace? 30 For we know him that hath said, Vengeance belongeth unto me, I will recompense, saith the Lord. And again, The Lord shall judge his people. 31 It is a fearful thing to fall into the hands of the living God.
Anybody wants to say that the one time sacrifice for sin at the cross wasn't good enough? Better reread that consequence again above.
With all of their words and practises, there is nothing simple about the sacraments, the Eucharist nor the Mass that any believer should be a part of.
1 Corinthians 15:33 Be not deceived: evil communications corrupt good manners. 34 Awake to righteousness, and sin not; for some have not the knowledge of God: I speak this to your shame.
Hebrews 10:9 Then said he, Lo, I come to do thy will, O God. He taketh away the first, that he may establish the second. 10 By the which will we are sanctified through the offering of the body of Jesus Christ once for all. 11 And every priest standeth daily ministering and offering oftentimes the same sacrifices, which can never take away sins: 12 But this man, after he had offered one sacrifice for sins for ever, sat down on the right hand of God; 13 From henceforth expecting till his enemies be made his footstool. 14 For by one offering he hath perfected for ever them that are sanctified. 15 Whereof the Holy Ghost also is a witness to us:
You having the Holy Ghost means there is no more continual sacrifice for sins that would mimick anything of the Old Covenant as a necessity at all.
Titus 1:15 Unto the pure all things are pure: but unto them that are defiled and unbelieving is nothing pure; but even their mind and conscience is defiled. 16 They profess that they know God; but in works they deny him, being abominable, and disobedient, and unto every good work reprobate.
Believers in the RCC and catholicism need to leave the RCC now if they wish to declare their faith in Jesus Christ that they are saved and to abstain from the sacrament called the Eucharist which is nothing short but an idol.
1 Corinthians 10:14 Wherefore, my dearly beloved, flee from idolatry. 15 I speak as to wise men; judge ye what I say. 16 The cup of blessing which we bless, is it not the communion of the blood of Christ? The bread which we break, is it not the communion of the body of Christ? 17 For we being many are one bread, and one body: for we are all partakers of that one bread. 18 Behold Israel after the flesh: are not they which eat of the sacrifices partakers of the altar? 19 What say I then? that the idol is any thing, or that which is offered in sacrifice to idols is any thing? 20 But I say, that the things which the Gentiles sacrifice, they sacrifice to devils, and not to God: and I would not that ye should have fellowship with devils. 21 Ye cannot drink the cup of the Lord, and the cup of devils: ye cannot be partakers of the Lord's table, and of the table of devils. 22 Do we provoke the Lord to jealousy? are we stronger than he?
2 Corinthians 6:16 And what agreement hath the temple of God with idols? for ye are the temple of the living God; as God hath said, I will dwell in them, and walk in them; and I will be their God, and they shall be my people. 17 Wherefore come out from among them, and be ye separate, saith the Lord, and touch not the unclean thing; and I will receive you. 18 And will be a Father unto you, and ye shall be my sons and daughters, saith the Lord Almighty.