I believe there are two separate questions entangled here, which
should probably be addressed separately.
1. Is there an organization, movement, denomination, church or
whatever entity that has a special identity, mission, and message for
this time in the world's history, as predicted by Revelation?
2. Does salvation depend on membership within that entity?
I like the treatment of the 1st question here:
Search for the True Church:
http://www.amazingfacts.org/Resources/Download/PBLib/BK-STC.pdf
The Bride of Christ:
Video:
http://www.amazingfacts.org/FreeStuff/BibleStudies/StudyGuides/tabid/105/ctl/ViewMedia/mid/453/IID/2-23/LNG/en/7/The-Bride-of-Christ/SC/L/Default.aspx
Study Gude:
http://www.amazingfacts.org/FreeStuff/BibleStudies/StudyGuides/tabid/105/ctl/ViewMedia/mid/453/IID/2-23/LNG/en/7/The-Bride-of-Christ/SC/R/Default.aspx
Here's an answer I found recently for the 2nd question:
"The advancement of the church is retarded by the wrong course of
its members. Uniting with the church, although an important and
necessary act, does not make one a Christian nor ensure salvation. We
cannot secure a title to heaven by having our names enrolled upon the
church book while our hearts are alienated from Christ. We should be
His faithful representatives on earth, working in unison with Him.
"Beloved, now are we the sons of God." We should keep in mind this
holy relationship and do nothing to bring dishonor upon our Father's
cause.
Our profession is an exalted one. As Sabbathkeeping Adventists we
profess to obey all God's commandments and to be looking for the
coming of our Redeemer. A most solemn message of warning has been
entrusted to God's faithful few. We should show by our words and works
that we recognize the great responsibility laid upon us. Our light
should shine so clearly that others can see that we glorify the Father
in our daily lives; that we are connected with heaven and are joint
heirs with Jesus Christ, that when He shall appear in power and great
glory, we shall be like Him." {4T 16}
So joining the church is "an important and necessary act," but we also
need to be united with Christ.