Will there be a limit on charitable donations in 2018? I pay tithes and offerings to my church. Will there be a limit on how much I give to the church?

You can give as much as you want to your church, or to any other charitable organization.  There is no limit to GIVING.

However, depending on your specific circumstances, your charitable contributions may not reduce the amount of tax on your tax return.

The upper limit for cash, for all cash charitable donations is 50% of your AGI.  (60% for 2018)

But...the thing you may be referring to is that the Standard Deduction is being doubled. Thus it is possible that your charity/church donations will not be used unless they (plus all your other itemized deductions) exceed the new Standard Deduction levels

So if your itemized Deductions don't exceed the new Standard Deduction, then the Sd Ded is used instead.  Check your 2017 Itemized Deductions to see if they exceed the new Std Deduction

I think some folks are going to be caught by surprise when they do their 2018 returns as a result of this.

...yeah...I'll be amused.

TP: But my itemized deductions total  $18,000, don't we get a Federal income deduction for that anymore?
Me: ...........so you don't want to use the larger $24,000 Standard deduction now?  That can be arranged, but you can't use both.

TP: What happened  my $4,050 Personal Exemption?