The court has said they're hoping to visit the issue as soon as they can.
One (and only one) member of the court signaled an interest to return to Obergefell v. Hodges (the same-sex marriage case). That is far from "the court has said."
Don't blame Congress for taking time to address the will of their constituents in the face of unelected activist judges.
While I would agree that I can understand Congress wishing to safeguard it in case the Supreme Court does sometime down the line overturn it, I deny that it would be activist for the Supreme Court to do so, as such a thing is returing it to the democratic process. It seems to me that, when it comes to judicial review (the assessment of a law as constitutional or not), judicial activism would only be possible in cases where you strike down a law, thereby removing it from the democratic process. Between Obergefell v. Hodges and a hypothetical decision overturning it, if there is any judicial activism, it would be in Obergefell v. Hodges.
This is not to say that striking down a law is judicial activism; that would be silly. But when it comes to judicial review, I feel only decisions that strike down laws can properly be regarded as candidates for judicial activism.
I believe it was a single Justice not the entire Court that talked about revisiting the issue.
Yes, this is correct. And given the extent to which the majority opinion attempted to set the case apart from Obergefell v. Hodges, it seems rather unlikely they are particularly interested in revisiting Obergefell and similar precedent.
Until the Supreme Court rules otherwise there is no problem. The Congress does not need to pass laws guaranteeing what a Court has proclaimed to be a constitutional right unless and until there would be a ruling from the current Court that previous activist Justices were wrong to invent a right to a government sponsored marriage as no such right exists.
This, however, is not correct. While it is true there is no need to pass laws guaranteeing what the Supreme Court has ruled so long as the ruling stands, the question does remain: What if the Supreme Court changes its mind? The Supreme Court (absolutely correctly in my view) overturned Roe v. Wade. Had congress sometime in the interim passed a law codifying a right to an abortion of some kind, then that law would have remained in force. It makes a lot of sense to think "okay, in case that happens again, let's put this into the law so that if it's overturned, it won't change things."
If the court does take up this issue, which is unlikely IMO, and reverses the previous ruling it is likely to rule that the power to issue a government marriage license belongs to the States not the federal government so any federal laws passed now concerning who can or cannot be married would be considered unconstitutional. This is no more than virtue signaling by the Congress as it doesn't actually safeguard gay marriage at all. The only safeguard to gay marriage, should the previous ruling be reversed in that way, would be by doing so through State laws.
I do not see how this law would be judged to exceed the power of the federal government. When the Supreme Court ruled on the Defense of Marriage Act (a law that went the other way, being against same-sex marriage) in United States v. Windsor, I don't believe anyone, dissent or majority, thought it exceeded the power of the federal government; the debate at hand was whether it violated the Equal Protection and/or Due Process Clauses.
Indeed, the Respect for Marriage Act (the new bill in question protecting rights to same-sex marriage) does not do anything in regards to the federal government granting marriage licenses; what it does is that it prohibits states from not recognizing marriages performed in another state on the basis of "sex, race, ethnicity, or natural origin of the individuals" (in other words, a state could refuse to recognize a marriage of another state based on something like age or number of people in the marriage, but could not refuse to recognize it based on gender or race of the couple). This would seem to fall easily within the power of the federal government through the Commerce Clause, which grants congress power to regulate commerce among the states. Now, there has of course been debate as to how far this extends (note it says among the states--it says congress can regulate interstate commerce, but not intrastate commerce, and exactly what counts as which is the what prompts all the debates). However, even under a more narrow reading of the Commerce Clause, it seems to me this would easily qualify as an exercise of the Commerce Clause.