The only thing that counts is faith expressing itself through love.
I immediately zoom in on the "expressing" part... that's the part that calls for action. That's what counts, where it's at... the active expression of love.
However, a closer look reveals that the phrase "expressing itself through love" is a description linked to the main object of the sentence: faith. The only thing that counts is faith.
My faith is in God and in His son Jesus. This faith means that I accept every aspect of His character. Such as:
God is love. 1 Jn 4:16
God is truth. Jn 14:6
God is holy. Lev 11:44
I cannot have faith in a God who loves me and live as if my life is insignificant. This denies the God who calls me His beloved.
I cannot have faith in a God of truth and think that His promises do not apply to me. This denies the God who has given me "these very great and precious promises." 2 Pet 1:4
I cannot have faith in a God of holiness and believe that He will "understand" my weakness if I harden my heart to His call. This denies the need for Jesus' death as a way to bring me back to God.
I could go on. Faith is not a mental mind-game, a "yes, I believe in God." It overtakes every aspect of my life, every thought, every decision, every action.
Everything that does not come from faith is sin.
Whatever thoughts I think, decisions I make, actions I take, if they are not rooted and grounded in true faith in a God of love, truth, and holiness, they are sinful. They cannot stand. They will not stand.
I join the father in Mark 9:24, pleading:
I do believe; help me overcome my unbelief!