<human>: Provide a brief overview of the text.

I was contacted out of the blue for an interview at a major engineering firm.  I work for a small firm right now, and I do wonder if making the leap to the larger firm may offer more opportunities down the road.

The thing is, I really love the place I'm at, but I don't know that I want to plant roots where I'm at and this new offer is enticing.  But I don't really want to consider it without waiting to see what shakes out at the end of this year at my current job.  I'm in line for a substantial raise at the end of the year, and I feel like it will  meet or beat whatever offer I get from the large firm (judging by their reported glassdoor salaries).

I don't want to decline the offer outright, but I wouldn't feel right going behind my current employer's back when they have treated me extremely well over these past few years.

The work I do is highly specialized and I've already turned a few other offers down, but none at such a major player in my industry.

How can I decline the offer while still leaving the door open for a later time?  Basically, I want to give my current job first crack at keeping me because I really love the work here, even in spite of not loving the city that the job is in.
<bot>: potentially great job offer, but already have a great job and don't want to risk it without hearing what current job will offer in an expected substantial raise at the end of the year.