Sola Christus, or Christ Alone, is more than the fact that He is in relation to salvation.
He is not a cheerleader, cheering you on to eternal life but the giver of it upon your faith (John 5:24).
He is more than just a Savior to which every knee shall bow and every tongue confess the He is Lord (Philippians 2:9-11)
And He is not just one way to the Father as if He's is one of 10 options but THE way to God in more than just a path way to heaven. He is the one mediator between God and man
From the beginning, God instituted High Priests to bridge the gap between sinful man and a holy God who cannot allow sinners into His presence; but mediatorship requires a special kind of high priests and the man Melchizedec, was that high priest no other in history could meet, until Jesus Christ.
Jesus, because He is God, is by nature holy and just. However, as man, He knows fully our struggles as He Himself is tempted at all points yet did not sin (Hebrews 4:15). It is for that reason, He became our advocate in 1 John 2:1, and fulfilled the order of Melchizedec .
Prior to the Reformation, the laity and the clergy prayed to Saints and Angels as they serve as "intercessors" to God on their behailf. But if Jesus was the one who alone fulfilled the order of Melchizedec as detailed in Hebrews 7-9, then why are they praying to Saints and Angels?
Sola Christus is a stand directly against 1 Timothy 2:5. It clearly states that there is ONE mediator between God and Man, the man Christ Jesus. To pray to the Angels and Saints is to defeat the purpose of Christ's coming.
It is also idolatrous as it deviates honor, reverence, and glory that could have all been to Christ... but instead goes to them.
Notice that when praying the Rosery, the Catholics say 10 "Hail Mary's" but only one "Our Fathers", and one ""Glory be's". And there are different kinds of prayers to different Saints and Angels just as what Pagans have done as they have different prayers to different kinds of gods and goddesses.