Three Solas
The source of authority for all matters pertaining to life and faith are the Holy Scriptures alone (Sola Scriptura), since Jesus declared, "[Father] Your Word is truth" (John 17).
This Word shows us that we are sinners completely unable to please God by our own efforts since we habitually and continually break His commandments in what we think, say, and do (and leave undone):
"by works of the law no human being will be justified [declared "innocent"] in His sight," for "all have sinned and fall short of the glory of God . . ." (Romans 3).
[Jesus] "was wounded for our transgressions. He was bruised for our iniquities. The punishment that brought us peace was upon Him, and by His wounds we are healed" (Isaiah 53).
So, since "to the one who does not work but trusts Him Who justifies the ungodly, his faith is counted as righteousness . . ." (Romans 4), we no longer live to please our sinful nature, nor do we try to earn God's favor. Instead, we show our thankfulness for His great mercy, living by God's grace alone (Sola Gratia), through faith alone (Sola Fide), in Christ alone (Solus Christus)!
Sola Gratia + Sola Fide + Sola Scriptura
Solus Christus!