sarvopādhi-vinirmuktaṁ tat-paratvena nirmalam hṛṣīkeṇa hṛṣīkeśa- sevanaṁ bhaktir ucyate

To make a show of devotional service will not help one. One must be a pure devotee following the devotional process; then one can convert others to devotional service. Sri Caitanya Mahaprabhu practiced devotional service and preached (apani acari' bhakti karila pracara). If a preacher behaves properly in devotional service, he will be able to convert others. Otherwise, his preaching will have no effect.