Mark 9:41

By which He shows, that he of whom John had spoken was not so far separated from the fellowship of the disciples, as to reject it, as a heretic, but as men are wont to hang back from receiving the Sacraments of Christ, and yet favour the Christian name, so as even to succour Christians, and do them service only because they are Christians. Of these He says they shall not lose their reward; not that they ought already to think themselves secure on account of this good will which they have towards Christians, without being washed with His baptism, and incorporated in His unity, but that they are already so guided by the mercy of God, as also to attain to these, and thus to go away from this life in security.

(Vict. Ant. e Cat. in Marc.) And that no man may allege poverty, He mentions that, of which none can be destitute, that is, a cup of cold water, for which also he will obtain a reward; for it is not the value of the gift, but the dignity of those who receive it, and the feelings of the giver, which makes a work worthy of reward.

Not only will I not forbid him who works miracles in My name, but also whosoever shall give you the smallest thing for My name's sake, and shall receive you, not on account of human and worldly favour, but from love to Me, shall not lose his reward.