When a person makes a vow to do something it depends on whether they make that vow to people or to God.
Deu 23:21 When thou shalt vow a vow unto the LORD thy God, thou shalt not slack to pay it: for the LORD thy God will surely require it of thee; and it would be sin in thee.
Deu 23:22 But if thou shalt forbear to vow, it shall be no sin in thee.
If a person vows to God to do something then they should do it for if not then it is a sin.
But if you do not vow it then it is not sin which it is obvious that this is an option for the person.
Which means God did not require it of them until they made the vow.
So if you vow to God to donate so much to the Church and you do not do it then it is sin.
But I believe Ananias and his wife were an example for the early Church and God does not punish a person by death today but it is still a sin that they need to repent of.
It is probably better not to vow to God that you will do anything so then if you do not own up to it you will not have sinned.
Ecc 5:4 When thou vowest a vow unto God, defer not to pay it; for he hath no pleasure in fools: pay that which thou hast vowed.
Ecc 5:5 Better is it that thou shouldest not vow, than that thou shouldest vow and not pay.
It is better to not vow than vow and not pay it.
Act 5:1 But a certain man named Ananias, with Sapphira his wife, sold a possession,
Act 5:2 And kept back part of the price, his wife also being privy to it, and brought a certain part, and laid it at the apostles' feet.
Act 5:3 But Peter said, Ananias, why hath Satan filled thine heart to lie to the Holy Ghost, and to keep back part of the price of the land?
Act 5:4 Whiles it remained, was it not thine own? and after it was sold, was it not in thine own power? why hast thou conceived this thing in thine heart? thou hast not lied unto men, but unto God.
Peter said the land was their own and in their own power to do what they want with the land which means Ananias and his wife could of sold the land and kept all the money for themselves because God did not require the money of them.
But they vowed unto God to give all the money to the Church but kept some of the money so it became a sin unto them and they lost their life because of it.
If they had vowed to the apostles they would do it and did not vow unto God they could of kept some of the money and it would of been alright for they would of lied to people and not to God.
But I do not believe God causes people to collapse and die today if they vow and do not keep it but it is still a sin that needs to be repented of.
If a person vows to God and does not keep it then then they lied to God but He understands that some people might of been hasty and did not think it through or maybe it was out of their control and they thought they could do it but could not but actually tried to come through on the vow.
But Ananias and his wife knew for sure they would get money for their land and it was a sure deal but they vowed to God and kept some of the money so they sinned.
It is obvious that they vowed to God and did not keep that vow and that they said they would give all the money to the Church for if they vowed to the disciples and kept some of the money they would not of died.
And they could of sold the land and kept all the money and not died if they did not vow to God for He did not require that they give it to the Church but it was their own land and in their own power to do whatever they wanted to do with that land whether not sell it or sell it and keep all the money.