18 And, Whosoever shall swear by the altar, it is nothing; but whosoever sweareth by the gift that is upon it, he is guilty. 
18 You also say, 'If anyone swears by the altar, it means nothing; but anyone who swears by the gift on the altar is bound by that oath.'
18 And you say, 'If anyone swears by the altar, it is nothing, but if anyone swears by the gift that is on the altar, he is bound by his oath.'
18 And what about this piece of trivia: 'If you shake hands on a promise, that's nothing; but if you raise your hand that God is your witness, that's serious'?
18 And, 'Whoever swears by the altar, it is nothing; but whoever swears by the gift that is on it, he is obliged to perform it.'
18 And you say that to swear 'by the altar' is not binding, but to swear 'by the gifts on the altar' is binding.
Matthew Henry's Commentary on Matthew 23:18
Commentary on Matthew 23:13-33
(Read Matthew 23:13-33)
The scribes and Pharisees were enemies to the gospel of Christ, and therefore to the salvation of the souls of men. It is bad to keep away from Christ ourselves, but worse also to keep others from him. Yet it is no new thing for the show and form of godliness to be made a cloak to the greatest enormities. But dissembled piety will be reckoned double iniquity. They were very busy to turn souls to be of their party. Not for the glory of God and the good of souls, but that they might have the credit and advantage of making converts. Gain being their godliness, by a thousand devices they made religion give way to their worldly interests. They were very strict and precise in smaller matters of the law, but careless and loose in weightier matters. It is not the scrupling a little sin that Christ here reproves; if it be a sin, though but a gnat, it must be strained out; but the doing that, and then swallowing a camel, or, committing a greater sin. While they would seem to be godly, they were neither sober nor righteous. We are really, what we are inwardly. Outward motives may keep the outside clean, while the inside is filthy; but if the heart and spirit be made new, there will be newness of life; here we must begin with ourselves. The righteousness of the scribes and Pharisees was like the ornaments of a grave, or dressing up a dead body, only for show. The deceitfulness of sinners' hearts appears in that they go down the streams of the sins of their own day, while they fancy that they should have opposed the sins of former days. We sometimes think, if we had lived when Christ was upon earth, that we should not have despised and rejected him, as men then did; yet Christ in his Spirit, in his word, in his ministers, is still no better treated. And it is just with God to give those up to their hearts' lusts, who obstinately persist in gratifying them. Christ gives men their true characters.