Ourselves we do inter with sweet derision.
The channel of the dust who once achieves
Invalidates the balm of that religion
That doubts as fervently as it believes.
(F.1449/J.1144)
[1] we:: Christians who suffered from the "doubts" in line four. inter, sweet derision:: buried together with all the sufferings, but it's sweet to meet God.
[2] channel of the dust:: a Christian life; "God formed man of the dust of the ground" (Genesis 2:7); "for dust thou art, and unto dust shalt thou return" (Genesis 3:19).
[3] the balm of that religion:: Christian belief should soothe all pains. Invalidates:: Christians don't get the balm due to the doubts of God.
[4] doubts:: sufferings as the test of God who doubts on Christians' faith. "The LORD trieth the righteous" (Psalms 11:5). it believes:: "that religion" believes God and His test fervently.