In the closing words of Mark 9 , Jesus exhorts, "Have salt in yourselves." In its context I believe this is a call to purifying self-examination. We are to actively purify ourselves by examining our motives and actions in the light of Jesus' call to humble service in his kingdom. If his followers would do this then pride (the source of contention among his disciples, Mark 9:34) would be tempered and we will "be at peace with one another."
I came across the following from this morning's entry of Spurgeon's "Morning and Evening." He gives a helpful and humbling means by which we might do this:
"June 12 | Morning | 'Thou art weighed in the balances and art found wanting.' - Daniel 5:27
It is well to frequently weigh ourselves in the scale of God’s Word. You will find it a holy exercise to read some psalm of David, and, as you meditate upon each verse, to ask yourself, 'Can I say this? Have I felt as David felt? Has my heart ever been broken on account of sin, as his was when he penned his penitential psalms? Has my soul been full of true confidence
in the hour of difficulty as his was when he sang of God’s mercies in the cave of Adullam, or in the holds of Engedi? Do I take the cup of salvation and call upon the name of the Lord?' Then turn to the life of Christ, and as you read, ask yourselves how far you are conformed to his likeness. Endeavor to discover whether you have the meekness, the humility, the lovely spirit which he constantly inculcated and displayed. Take, then, the epistles, and see whether you can go with the apostle in what he said of his experience. Have you ever cried out as he did-'O wretched man that I am! who shall deliver me from the body of this death?' Have you ever felt his self-abasement? Have you seemed to yourself the chief of sinners, and less than the least of all saints? Have you known anything of his devotion? Could you join with him and say, 'For me to live is Christ, and to die is gain'? If we thus read God’s Word as a test of our spiritual condition, we shall have good reason to stop many a time and say, 'Lord, I feel I have never yet been here, O bring me here! give me true penitence, such as this I read of. Give me real faith; give me warmer zeal; inflame me with more fervent love; grant me the grace of meekness; make me more like Jesus. Let me no longer be "found wanting," when weighed in the balances of the sanctuary, lest I be found wanting in the scales of judgment.' 'Judge yourselves that ye be not judged.'”
In other words, "have salt in yourselves."