Welcome those who are weak in faith, but not for the purpose of quarreling over opinions.  Romans 14:1

Pick your quarrels carefully. and use gentle words instead of harsh, cutting, and cruel.  You are helping the weak into the consecrated life. Time is on your side. Patience is your advantage. Refuse to get discouraged. Be certain that our Lord does not put all the responsibility for maturing the weak one’s spirituality all on you– He orchestrates other believers too.

Paul defines those weak in faith– they use the world’s ethics as a life template in lieu of immersion in Christ.  The choice to rely on the Holy Spirit’s guidance in the heart and the conscience within the weak believer is like the ebb and flow of a river– sometimes there is a rapid flowing interest in staying in the Way of Christ and other times there is a pooling of fall-back onto stagnant former ways.

Those who are weak in faith need Good News teachings as they grow to maturity as Christians.  Choose the times in which you speak up for Christ.  When a quarrel erupts it may be over opinions and not core Christianity and if so then give up, back away, and rest if the quarrel is about options.  

Trust God’s plan for those who are weak in the faith– His plan of sanctification; the maturing of faith through faith’s testing and endurance.  As you understand your process of sanctification so you will understand that of the weak.