"The mystery of the Holy Trinity is the most fundamental of our faith. On it, everything else depends and from it, everything else derives. Hence the Church's constant concern to safeguard the revealed truth that God is One in nature and Three in Persons." ("Father" John A. Hardon, SJ found at the Catholic Education Resource Center) JA Hardon is a member of SJ - "Society of Jesus", also known as Jesuit Order
"And never forget that the precise goal of all apostolic service is to lead all people to communion with the Most Holy Trinity." -Pope John Paul II, New Orelans (United States) Saturday, 12 September 1987
There is one God
That one God consists of three coeternal persons, namely the Father, Son, and Holy Spirit.
Each of the three persons is God
All of the three persons have the same nature
The God of the 7th-day Sabbath says, "... I gave them my sabbaths, to be a sign between me and them, that they might know that I am the LORD that sanctify them."(Ezekiel 20:12)
Considering Revelation 7,13, & 14 it seems to me that the seal of God and the mark of the beast are all about who each individual is worshiping - either the God of the seventh-day Sabbath or the god of the 1st-day sabbath. If that is true, then I have a question for my SDA friends:
In light of the comparison above, what makes you think that the beast who's "deadly wound was healed" cares what day you worship on when you already worship its declared god - as defined in the Catechism?
As for me and my house, we want the seal of the Living God in our foreheads, signifying that's who we worship. So, we will worship the God of the 144,000, as defined by the Bible:
Revelation 14:1 And I looked, and, lo, a LAMB stood on the mount Sion, and with him AN HUNDRED FORTY AND FOUR THOUSAND, having HIS FATHER'S NAME written in their FOREHEADS.
Revelation 7:2 And I saw another angel ascending from the east, having the SEAL of the LIVING GOD: and he cried with a loud voice to the four angels, to whom it was given to hurt the earth and the sea, 3 Saying, Hurt not the earth, neither the sea, nor the trees, till we have SEALED THE SERVANTS OF OUR GOD IN THEIR FOREHEADS. 4 And I heard the number of them which were sealed: and there were sealed AN HUNDRED FORTY AND FOUR THOUSAND...
Matthew 16:16 And Simon Peter answered and said, Thou art the Christ, THE SON OF THE LIVING GOD. 17 And Jesus answered and said unto him, Blessed art thou, Simon Barjona: for flesh and blood hath not revealed it unto thee, but MY FATHER which is in heaven.
Jesus said that true worshippers shall worship the Father in spirit and in truth: for the Father seeketh such to worship him. (John 4:23)
Here is a more-detailed explanation