Not only spread the word, but line the pockets. Which is why ZZD started carrying sporting events, to generate a revenue while hoping the fans of the teams would stay around after the game to experience the word of the Lord. Low overhead, yes. However, most people figured this out, but I digress.
I'd not assume the idea was to line their pockets, but maybe to pay some bills and make an income for their corporation ( I don't know if they are considered a non-profit or not, but that would also make a difference), which is what all radio stations try to do. However, your comment brings up another point that needs to be made in regards to religious radio. Many assume it is a evanglistic tool. Sometimes it might work that way as you suggested that someone listening to a game on WZZD would then stay and listen to some CCM music and get saved. More often than not, the only people who listen to religious stations are those of that same faith. So CCM, dollar a hollar, Family Radio, hymns stations pull in those of faith that like that particular format. Those who are not of that faith will tune out as soon as they pick up on the fact that the music is religious. So my guess is WZZD aired sports to help pay the bills rather than as a evangelistic tool.
The problem for WZZD being a music station is that CCM music appeals to a younger demo than hymns or preachers. So being on AM is a liability. If WZZD was on FM, then they probably would do just fine with CCM and CCM gold. The only music you hear on AM today is ethnic music, hymns, Big Band, and Oldies (these last two are becoming very hard to find anywhere AM or FM). All other music is on FM. Maybe WZZD could get Harold Camping to sell them their Family Radio FM station (WKDN 106.9 Camden) to them, then they'd have a chance to succeed with music in the Philly/Wilmington/Trenton area.
Of course, as non-comms do not show on Arbitron 12+ numbers, we don't know how well WDKN (Family Radio) is doing, but as they are listener supported like WHYY-FM or WRTI they must be pulling in enough listeners who contribute to keep that powerful FM signal running and on the air. My guess is if Family Radio ever decides to sell WDKN there will be some major money to be made as that station has a strong signal from Trenton to Wilmington making it a viable station for the Philly market and Wilmington and Trenton. I know a few years ago Family Radio sold an FM station on the West Coast and bought an AM station, because it was less expensive to operate, so who knows, maybe someday Family Radio will move to 990 and Salem will move to 106.9.