"Judge not, that you may not be judged, For with what judgment you judge, you shall be judged: and with what measure you mete, it shall be measured to you again. Any why seest thou the mote that is in thy brother's eye; and seest not the beam that is in thy own eye? " Matthew 7:1-3
"Beloved, believe not every spirit, but try the spirits whether they are of God: because many false prophets are gone out into the world." -- 1 John 4:1
We are to correctly weigh and discern the actions of others. By their fruit are all men known.
However, we are not to judge their salvation, which is of God alone.
Big difference.