Paul writes, "for when their passions draw them away from Christ, they desire to marry and so incur condemnation for having abandoned their former faith" (1 Timothy 5:11). This not only sounds harsh, it seems to contradict what he wrote to the Roman believers that a widow can remarry (Romans 7:1-4). Therefore we must look more closely at what he said to Timothy.
A couple of days ago, we referred to Anna who as an example of a widow being supported by the church. Her entire life was dedicated to service in the temple ( Luke 2:36). We are instructed in the book of Ecclesiastes that we should be careful that we do not break a vow to God and incur judgement (Ecclesiastes 5:4-7).
So Paul is not restricting young widows from marrying, in fact he says specifically that they should marry in (1 Timothy 5:14). He is reasoning that young women still have a desire to marry which will most likely result in breaking their vow to remain single. Therefore they should never make such a vow.
When Paul writes "They have cast off their first faith" he is not referring to the faith if salvation, but refers to the faith of their vow to remain single.