If we are saved before partaking the Lord's Supper then partaking of the Lord's Supper is useless. Do you agree?
a. If one has received the gift of the Holy Spirit, they have the
sins (Acts 2:38).
b. Cornelius received the gift of the Holy Spirit in Acts 10:45 before he was water baptized in Acts 10:48.
c. Therefore Cornelius already had the forgiveness of sins before he was water baptized.
I'd like to see how "a" and/or "b" which prove the truth of "c" is in error.
The Bible states that failure to participate in the memorial of our Lord's death, the Lord's Supper can led a person to lose their soul. "Then Jesus said to them, "Most assuredly, I say to you, unless you eat the flesh of the Son of Man and drink His blood, you have no life in you. Whoever eats My flesh and drinks My blood has eternal life, and I will raise him up at the last day"" (John 6:53-54). However, the memorial of Jesus' death is not a single act, but one that is continually done each first day of the week. "For as often as you eat this bread and drink this cup, you proclaim the Lord's death till He comes" (I Corinthians 11:23). Thus partaking of the Lord's Supper is an act of obedience that a saved person does as he journey's through life. If he fails to be obedient to this or any other command, he will lose his life. If he remains obedient he will have eternal life. "For we have become partakers of Christ if we hold the beginning of our confidence steadfast to the end" (Hebrews 3:14).
The comparison to the Lord's Supper does not tell us whether God requires baptism in water to be saved from our sins.
In regards to the salvation of Cornelius and his household, it has been addressed in length in When Was Cornelius Saved?